Poly(N-vinylcaprolactarn) (PVCap) has previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). The inhibition performance of LDHI is known to be influenced by molecular weight (M-w) and molecular weight distribution. In this study, PVCaps were synthesized by two different methods. The first method; reversible addition fragmentation chain transfer (RAFT) polymerization, was used to prepare PVCap with a narrow molecular weight distribution (about M-w/M-n < 1.5), which is close to theoretical values. The second method) free radical polymerization (FRP), was used to obtain a broad molecular weight distribution (about M-w/M-n > 1.5). In a semi-batch stirrer reactor, hydrate inhibition performance of PVCap was evaluated. It was found that the inhibition performance was increased when the PVCap molecular weight decreased. PVCap with the narrower molecular weight distribution also showed the better inhibition performance.