Green colored rats that can only be spawned by a Big Green Rat. They are similar to regular rats, but they don't drop rads and have less HP. However, green rats do drop pickups, which means that this enemy is great for farming ammo or health via Rabbit Paw or Blood Lust. They die on their own after 30 seconds from being spawned.
- In the game code, Small Green Rats are referred to as "Fast Rats".
- With Melting it is possible to farm extra rads rads out of Small Green Rats since his passive makes them drop one rad each. However, Big Green Rats will become enraged after spawning too many rats, so this cannot be done indefinitely.
- The look of Small Green Rats was slightly changed in update #93 which made them easier to distinguish from regular Rats.