Recently, much attention has been paid to human retinoblastoma since it provide a good model system for studying mechanisms underlying cell growth, differentiation, proliferation, and apoptosis, and for developing cancer therapy. However, until now it is unclear whether purinergic receptors are involved in the calcium mobilization in the retinoblastoma cells. In this regard, we measured possible purinergic signaling in WERI-Rb-1 cells using $Ca^{2+}$ imaging technique and RT-PCR method. ATP-induced $[Ca^{2+}]_i$ transients was maintained to about $90.7{pm}1.0%$ of the control (n=48) even in the absence of extracellular calcium. The ATP-induced intracellular calcium response was only attained to $10.4{pm}1.8%$ (n=55) of peak amplitude of the control after preincubation of 1 ${mu}MU-73122$, a PLC inhibitor, but it was not affected by 1 ${mu}MU-73343$, a inactive form of U-73122. And also ATP-induced $[Ca^{2+}]_i$ rise was almost attenuated by 20 ${mu}M$ 2-APB, a putative $IP_3$ receptor inhibitor. Two subtypes of $IP_3$ receptor $(IP_{3-1}R,;IP_{3-2}R)$ were identified by a RT-PCR method. These findings suggest that purinergic stimuli can cause calcium mobilization via $PLC-IP_3$ pathway after the activation of P2Y receptors in the retinoblastoma cells, which may play important roles in cell proliferation, differentiation, growth, and cell death.