Most of the time, Chopper is a toddler-sized human/reindeer hybrid, but his Devil Fruit abilities allow him to change his appearance depending on the situation. Chopper's left antler is braced at the base by a metal plate because it was reattached after being broken during his search for the Amiudake when he was younger (where he thought the Amiudake can cure Hiluluk's disease) and ran into the leader of his old herd, who severely injured him.[7] He usually wears a large pale red/pink fuzzy top hat with a sideways medical cross (given to him by Hiluluk) and a maroon pair of shorts. He also sometimes wears a blue backpack that has the same sideways medical cross as his hat. He also has a remarkable blue nose. As Oda's style evolved and many readers commented on how cute Chopper was, Chopper has been given a much more "chibi" like appearance, meaning that when in his preferred transformation (which he calls Brain Point), he has a larger head and eyes and a less defined muzzle than earlier in the series. Many female characters, such as Nami, Robin, Makino, Porche, Shakky, and Vivi find Chopper very cute. There are even males that find Chopper cute such as Foxy.

A running gag is that various characters in One Piece think Chopper is a tanuki (raccoon-dog, often simply translated as "a raccoon") while in his Brain Point or hybrid form. The word "tonakai", which is the Japanese word for "reindeer", is where the "Tony" in Chopper's name is derived from. His Heavy Point or human form is likewise mistaken for a gorilla (or an abominable snowman on his home island).