Two kinds of amphiphilic block copolymers, allyoxyl poly(ethylene glycol)-b-poly(L-lactide) and methoxyl poly(ethylene glycol)-b-poly(L-lactide-co-2-methyl-2-allyloxycarbonyl-propylene carbonate), were synthesized in a controllable manner. Radical mediated thiol-ene reaction was utilized to modify these two precursor block copolymers with three model mercaptans. Highly efficient and quantitative modification under UV light without adding any photoinitiators was observed by H-1 NMR spectra of the products collected at specific time points. The reaction rate was mainly dependent on molar ratio of thiol to vinyl in feeding. Quantitative transformation of the vinyl groups in both block copolymers was realized in 0.5-2 h when using excessive thiol with respect to vinyl. Using commercially available mercaptans, different functional groups were introduced into the block copolymers, thus realizing modular functionalization of target block copolymers. This method of functionalization effectively avoided traditional protection/deprotection procedures, thus greatly simplifying the process of functionalization. Precipitation and dialysis procedures were proved efficient to eliminate excess mercaptans, thus endowing the material with good biocompatibility.