The first season of Underground Ernie started airing on the 5th of June 2006. It lasted for 26 episodes.
- Pop Decoy - Jubilee lets slip his secret about pop star Sam 7 visiting International Underground while Bakerloo gets into pop music.
- Sir Clunkalot - Bakerloo tells tales of a ghost haunting Mystery Mansion and Ernie gets trapped in a suit of armour.
- Mr Rails Never Fails - Ernie has a cold leaving Millie in charge of the arrangements for Mr Rails' surprise party.
- Brooklyn and Rocky Two-Shoes - Brooklyn visits, bringing American athlete Rocky Two-Shoes with him.
- Pulling Together - The twins Hammersmith and City fall out when they learn they won't be able to watch the big football match together.
- Caught Purple Handed - A rather absent-minded explorer brings a rare plant to the Underground.
- Ernie's Big Trip - Paris visits while the trains fear that Ernie is leaving to run the French Underground instead.
- Finders Keepers - Mr Rails wins a luxury holiday but loses the golden ticket.
- The Magician's Assistant - Millie is given the chance of a lifetime to be Maestro the Magician's assistant.
- Cover Story - While Ernie tries to take some photos for Tunnel Times, Sydney convinces the trains to look cool and Bakerloo fears that Ernie's selling them off!
- Millie's Dream Day - Millie wins a dream day at International Underground so Mr Rails attempts to do her job while she's away.
- Mr Movie Jones - There's a case of mistaken identity when a film director goes to look at Sea Shell Bay as a potential location for his next film.
- Summer Breeze - The summer heat is unbearable, so Mr Rails and Ernie try to cool the Underground down. Meanwhile, Circle and the twins have a competition.
- Running Late - Victoria fears she may be headed for the scrap heap while Jubilee goes too fast and lands in trouble.
- Light At The End Of The Tunnel - The museum is at risk of closing down. While Victoria tries to advertise the museum, Mr Rails and Ernie make a great discovery.
- The Wreck Of Sea Shell Bay - Ernie's mischievous nephews Sam and Dan go on a school trip to Sea Shell Bay and uncover some hidden treasure.
- Catnapped - Circle helps Pippa find her missing cat Patch.
- Monster Mystery - Strange noises remind Bakerloo of a monster that was once rumoured to roam around the Underground.
- Bon Appetit - Famous chef extraordinare Marcel Le Magnifique arrives and Millie cooks a meal for him.
- A Change Is As Good As A Rest - Brooklyn gives the trains the idea of swapping lines for a day, causing widespread confusion all over the Underground.
- Elementary, My Dear Bakerloo! - The nature reserve is short of funds so Ernie hosts a jumble sale to sort things out. When the jumble goes missing, Bakerloo is on the case!
- The Magic Lamp - Ernie finds a magic lamp on his rounds.
- How Great The Art - Brooklyn returns, bringing an abstract piece of modern art with him. The trouble is, nobody wants it on their platforms.
- The Mayor's Visit - Hammersmith and City's brakes are malfunctioning while Mr Rails gets the wrong end of the stick when he hears of the Mayor giving an award to an Underground worker.
- Techno Trouble - Osaka arrives from Japan, bringing gifts for everyone. Jubilee ends up causing havoc with his hologram projector.
- Snow Go - When the trains are snowed in at the sheds, Moscow comes to the rescue.
All the visuals for this series were produced using the CGI software LightWave for the high cost of £4 million. ($7 million). The programme took a year to develop, 18 months to make and appeared on screen five years after creators John Deery and Sid Rainey first came up with the idea for the show. There were three times during the production process when everything was nearly lost.
Production started in October 2001 and finished in December 2003.
- Rumour has it that after a long period of being on the shelf, the BBC were planning to start airing this series in 2005, but delayed it after the London bombings of July in that year, at which point its broadcast would have been ill-timed.
- This series aired in several stages across 2006.
- The first twenty episodes aired throughout June.
- Another week of new episodes aired in November.
- The final episode went straight to DVD on November 20th 2006 before being broadcast on Christmas Day 2006.