Abstract Biocompatible materials using poly( N ‐vinylamide) derivatives are developed via a recently designed synthetic route. N ‐Vinylbenzamide (NVB) is synthesized as typical hydrophilic N ‐vinylamide monomer, then copolymerized with N ‐vinylformamide (NVF) by free radical polymerization, which can convert to cationic polyvinylamine unit by hydrolysis. Cell toxicity on the surface of copolymer films is investigated, revealing that poly( N ‐vinylamide) derivatives show biocompatibility regardless of the cationic ratio.