That depends. The smallest particle in the classic physics is te atom. In the modern physics is the quark (quark is the composition of an eletron).
WHAT IS THE SMALLEST PARTICLE
The quark
If you mean fundamental particles, I have bad news for you, they actually don't spin, well at least not like how you're probably thinking of it, e.g. like a basketball on a Globetrotter's finger. In...