Since papermaking process has been shifting to alkaline from acidic condition, exploring novel wet-end retention aids is considered to be of important resolution for modern papermaking industry. In this study vinylformamide-based cationic polymers were synthesized by polymerization of N-vinylformamide (NVF) followed hydrolysis of poly-N-vinylformamide (PNVF) and copolymerization of vinylformamide with quaternary ammonium cationic monomers, respectively. The characteristics of the resulting polymers was determined by using GPC and polyelectrolyte titration method. The polymers were then used as retention aid of rosin sizing in alkaline papermaking conditions. The results showed great potential of these vinylformamide-based cationic polymers as effective retention aids of alkaline papermaking. It was found that the retention performance is relative to the chemical structure of cationic portion and molecular weight of the polymer. Furthermore, the characterization of the retention behavior of the rosin size particles by the polymers using scanning electron microscope (SEM) and electron spectroscopy for chemical analysis (ESCA) revealed that the polymer molecules could physically form a special structure with rosin size particles so that the rosin size particles would still stable under alkaline conditions.