The neuropeptides oxytocin and arginine vasopressin (AVP) are involved in the regulation of social behavior and cognition. The current study analyzed the effect of oxytocin and AVP on proliferation and differentiation of serotonergic neurons (RN46A cells). Oxytocin did not affect, while 5-10 μM AVP decreased RN46A proliferation. Oxytocin did not significantly alter, while 10 μM AVP decreased the number of cells extending neurites. We found divergent effects of oxytocin and AVP in serotonergic neurons, underscoring their functional differences.