Poly(N-vinylpyrrolidinone) (PNVP) bearing 5-fluorouracil (5-FU) moieties was synthesised via a three-step method. Firstly, 5-FU reacted with formaldehyde to form a mixture of mono- and disubstituted hydroxymethyl-5-FUs. The mixture was then treated with allyl chloroformate to afford allyloxycarbonyloxymethyl-5-FUs. This reaction showed site-specificity: the hydroxymethyl goup at the N-1 position readily reacted with chloroformate whereas the N-3 hydroxymethyl group partially decomposed into formaldehyde and the amide group. 1-Allyloxycarbonyloxymethyl-5-FU (4) and NVP were copolymerized in dioxane using azobisisobutyronitrile as an initiator. The monomer reactivity ratios, r4 = 0.32 and rNVP = 0.97, were evaluated by both linear and non-linear methods.