Two charge monomers, namely 2-(methacryloyloxy)ethyl-trimethylammonium chloride (MAETAC) and sodium methacrylate (SMA), were incorporated into poly(ethylene glycol)-diacrylate (PEGDA) hydrogels to investigate the effects of surface charge on the proliferation and differentiation of osteoblasts. The physicochemical properties of the polymers were characterized, and MC3T3-E1 cells were seeded on the hydrogels to evaluate the effect of charge polarity and density on osteoblastic proliferation and differentiation. FTIR results revealed that the two charged monomers were successfully incorporated into PEGDA. The zeta potential of the hydrogels became more positive or negative with increasing concentration of MAETAC or SMA. The zeta potential of the charged hydrogels remained constant after immersion in culture medium for different time points. Other physicochemical properties such as surface morphology, swelling ratio in PBS, contact angle, and elastic modulus were not significantly different among each group with different concentrations of charge monomers incorporated into PEGDA. The modification of hydrogels with charge monomers not only improved osteoblastic proliferation but also upregulated alkaline phosphatase activity and the expression of osteogenic marker genes and relative growth factors. These findings indicate that, in contrast to charge polarity, the charge density would be more important to improve osteoblast-like cells proliferation and differentiation on the poly(ethylene glycol)-diacrylate hydrogel. The hydrogel can be designed by controlling the incorporation of charge monomers. This study provides a model to study the effect of charge on cell behavior.