The preparation of poly(L-lactide) nanoparticles via ring-opening polymerization (ROP) of L-lactide is conducted in non-aqueous emulsion. In this process, acetonitrile is dispersed in either cyclohexane or n-hexane as the continuous phase and stabilized by a PI-b-PEO, respectively, a PI-b-PS copolymer as emulsifier. The air and moisture sensitive N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)-2-ididazolidinylidene (SIMes) catalyzes the polymerization of L-lactide at ambient temperatures. Spherical poly(L-lactide) nanoparticles with an average diameter of 70 nm and a tunable molecular weight are generated. Hence, the non-aqueous emulsion technique demonstrates its good applicability toward the generation of well-defined poly(L-lactide) nanoparticles under very mild conditions.