The following is a list of episode summaries for the Sonic Underground television series. It first premiered in France on January 6, 1999 and aired on TF1 on the TF! Jeunesse block on Wednesdays and Sundays. The show later premiered in English in the UK on May 2, 1999 and aired on ITV1 on Sunday mornings. ITV1 aired the first 18 episodes in the original UK run before cancelling the show. Sonic Underground premiered in USA on August 30, 1999 and aired on the Bohbot Kids Network syndication block on weekday mornings at 6:00 AM Central Time.
While it was believed for a while that 65 episodes were made of which only 40 aired (since there were supposedly 65 planned), Ben Hurst, a main writer from Sonic the Hedgehog, who was also involved in Sonic Underground's production, stated in a chat at the Sonic Amateur Games Expo 2008 that only 40 were produced.
Season 1[]
01 - 01. Beginnings
01 - 02. Wedding Bell Blues
01 - 03. To Catch a Queen
01 - 04. Mobodoon
01 - 05. The Price of Freedom
01 - 06. Underground Masquerade
01 - 07. Tangled Webs
01 - 08. The Deepest Fear
01 - 09. Who Do You Think You Are
01 - 10. The Last Resort
01 - 11. Come Out Wherever You Are
01 - 12. Winner Fakes All
01 - 13. A Hedgehog's Home is Her Castle
01 - 14. Artifact
01 - 15. Bug!
01 - 16. Sonic Tonic
01 - 17. Friend or Foe?
01 - 18. Head Games
01 - 19. When in Rome...
01 - 20. The Jewel of the Crown
01 - 21. Three Hedgehogs and a Baby
01 - 22. Dunes Day
01 - 23. Mummy Dearest
01 - 24. Hedgehog in the Iron Mask
01 - 25. Six is a Crowd
01 - 26. Flying Fortress
01 - 27. No Hedgehog is an Island
01 - 28. Getting to Know You
01 - 29. New Echidna in Town
01 - 30. Harmony or Something
01 - 31. Country Crisis
01 - 32. Haircraft in Space
01 - 33. Healer
01 - 34. Sonia's Choice
01 - 35. The Big Melt
01 - 36. Sleepers
01 - 37. Bartleby the Prisoner
01 - 38. The Art of Destruction
01 - 39. The Pendant
01 - 40. Virtual Danger
Season 2[]
02 - 01. Miles "Tails" Prower is Back!
02 - 02. Sally Acorn's Here!
02 - 03. Sonic's Star Rock
02 - 04. Welcome Back Knuckles!
02 - 05. Manic's Bass-Drums Power Up
02 - 06. You Go, Sonia!
02 - 07. Tails' Singing Star
02 - 08. Sonic's Power Ring Returns
02 - 09. Dancing with the Mobius
02 - 10. Sally's Magical Music Star
02 - 11. Let's Road!
02 - 12. Knuckles at the Under-Holes
02 - 13. Manic's Got the Green-Power
02 - 14. Sonia and Sally's Wonderful Vacation
02 - 15. A Sonic Day Afternoon
02 - 16. Tails' Good Day
02 - 17. Sally at the Fashion Show
02 - 18. Sonic at the Mystic Mansion
02 - 19. Battle of the Boy Music
02 - 20. Knuckles and the Secret Emeralds
02 - 21. Chez Sonia
02 - 22. Manic's Lighting Thunder Crush
02 - 23. Sonic at the Wild Adventure
02 - 24. Girls Day Out
02 - 25. Tails' Lesson to the Rhythm
02 - 26. At the Hop
02 - 27. Thanks to Amy
02 - 28. Sally's Mission Competed
02 - 29. Sonic, Tails and Knuckles in the Three Musketeers
02 - 30. Knuckles' Weight Traning
02 - 31. Sonic and Tails and the Sidekick
02 - 32. Sonia's Dance Style
02 - 33. Manic's Cooler Bands
02 - 34. Sally and the Shiny Crystals
02 - 35. Tails at the Workshop
02 - 36. Rhythm of the Night
02 - 37. Knuckles and the Fireballs
02 - 38. Sonic, Sonia and Manic's Big Adventure
02 - 39. Sonic VS. Doctor Robotnik
02 - 40. Sonic and Friends Saves the Day