Can You Turn a Sim into an Animal in The Sims 3? No – But Pets Expansion Lets You Play as Animals

No, the base game does not allow you to change a Sim's species to an animal. There is no “Transform” interaction, and Create-a-Sim (CAS) lacks an “Animal” category for playable Sims.

Workarounds for Animal Gameplay

• The Sims 3: Pets Expansion: The intended way to play as animals. You can create, control, and play as Dogs, Cats, and Horses with unique needs and interactions.
• Custom Content (CC): Sites like Mod The Sims or The Sims Resource offer custom skins, ears, tails, and “feral” traits to give Sims an animalistic appearance. Warning: CC can cause graphical glitches or routing issues since the skeleton/rigging remains human.
• Cheats (Not Recommended): testingcheatsenabled true + Shift-click > “Modify Traits” can add hidden traits, but cannot change the fundamental Sim rig.

For a genuine animal experience, Pets is the only stable, feature-complete option.