PURPOSE. To explore the role of synapsin-Ia/b in visual cortical plasticity, the dynamic changes in total protein expression (T-) and conventional protein kinase C (cPKC)gamma-modulated phosphorylation (P-) levels of synapsin-Ia/b were observed in the developing visual cortex of mice. METHODS. The Western blot analysis was used to determine the levels of T-and P-synapsin-Ia/b at site of Ser9, 549, and 603; the cPKC gamma gene wild-type (cPKC gamma(+/+)) and knockout (cPKC gamma(-/-)) mice were applied to explore the modulation of cPKC gamma on synapsin-Ia/b phosphorylation status in visual cortex of mice at postnatal 7 to 60 days (P7-P60, n = 6 per group). RESULTS. The results showed that T-synapsin-Ia/b protein levels significantly increased at P14 to P35 and peaked at P42 to 60 (P < 0.001) in visual cortex when compared with that of P7 cPKC gamma(+/+) mice, and cPKC gamma(-/-) did not affect this pattern of T-synapsin-Ia/b protein expressions. For synapsin-Ia/b phosphorylation status, the levels of P-Ser9 and 603 synapsin-Ia/b significantly elevated at P21 to P28 (P < 0.05 or 0.001), and then went down and maintained at lower levels at P35 to P60 (P < 0.05 or 0.001) compared with P7 cPKC gamma(+/+) mice. In addition, the cPKC gamma gene knockout could significantly (P < 0.001) inhibit both the increase and decrease of P-Ser9 and 603 synapsin-Ia/b levels when compared with cPKC gamma(+/+) mice at P7 to P60. However, there were no significant changes of P-Ser549 synapsin-Ia/b in the developing visual cortex of both cPKC gamma(+/+) and cPKC gamma(-/-) mice at P7 to P60. CONCLUSIONS. These results suggested that both protein expression levels and cPKC gamma-modulated phosphorylation status at Ser9 and 603 of synapsin-Ia/b may play important role in developing visual cortex of mice.