Cationic polymer latex, poly(styrene/butyl acrylate-co- glycidyl methacrylate) [P(St/BA-co-GMA)], with core–shell structure was synthesized by a two-step semi-batch emulsion polymerization with styrene (St), butyl acrylate (BA) and glycidyl methacrylate (GMA) as monomers, cetyl trimethyl ammonium chloride (CTAC) as cationic surfactant, ethylene glycol dimethacrylate (EGDMA) as crosslinking agent, 2,2＇-azobis(2-methylpropionamidine) dihydrochloride (AIBA) as cationic initiator. The influence of surfactant dosage, initiator dosage, reaction temperature and time on the properties of latex were investigated. The monomer conversion of cationic latex reached 98.03% when the reaction proceeded under the following conditions: surfactant dosage of 6 %, initiator dosage of 0.5%, and 2 h reaction time at 80 ℃. The mean particle size and zeta potential of the resulted latex particles were 57.21 nm and +47.62 mV, respectively. The core-shell structure of latex was confirmed by Transmission Electron Microscope (TEM) and laser particle size analyzer. The latex was applied for hydrophobic modification of bagasse fibers. The water contact angle of the modified fiber was increased from 0°to 98°, compared with the untreated fiber, which indicated that the modified bagasse fibers were rendered hydrophobic by the cationic latex nanoparticles.