Monodispersed crosslinked cationic poly(4-vinylpyridine-co-butyl acrylate) [P(4VP-BA)] seed latexes were prepared by soapless emulsion polymerization, using 2,2'-azobismethyl(propionamidine)dihydrochloride (V-50) as an initiator and divinylbenzene (DVB) or ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The optimum condition to obtain monodispersed stable latex was investigated. It was found that the colloidal stability of the P4VP latex can be improved by adding an adequate amount of BA (BA/4VP = 1/4, w/w), and adopting a semicontinuous monomer feed mode. Subsequently, poly(4-vinylpyridine-co-butyl acrylate)/Poly(styrene-co-butyl acrylate) [P(4VP-BA)/P(ST-BA)] composite microspheres were synthesized by seeded polymerization, using the above latex as a seed and a mixture of ST and BA as the second-stage monomers. The effects of the type of crosslinker, the degree of crosslinking, and the initiators (AIBN and V-50) on the morphology of final composite particles are discussed in detail. It was found that P(4VP-BA)/P(ST-BA) composite microspheres were always surrounded by a PST-rich shell when V-50 was used as initiator, while sandwich-like or popcorn-like composite particles were produced when AIBN was employed. This is because the polarity of the polymer chains with AIBN fragments is lower than for the polymer with V-50 fragments, hence leading to higher interfacial tension between the second-stage PST-rich polymer and the aqueous phase, and between PST-rich polymer and P4VP-rich seed polymer. As a result, the seed cannot be engulfed by the PST-rich polymer. Furthermore, the decrease of T-g of the second-stage polymer promoted phase separation between the seeds and the PST-rich polymer: sandwich-like particles formed more preferably than popcorn-like particles. It is important knowledge that various morphologies different from PST-rich core/P4VP-rich shell morphology, can be obtained only by changing the initiator, considering P4VP is much more hydrophilic than PST. The zeta potential of composite particles initiated by AIBN in seeded polymerization shifted from a positive to a negative charge.