OBJECTIVE: To explore the mechanism of all-transretinoic acid (ATRA) increasing retinoblastoma (RB) sensitivity to vincristine, and the inhibiting effect of vincristine combined with ATRA treatment on the SO-RB50?cell proliferation. METHODS: SO-RB50?cells were cultivated by routine culture method. Different concentrations of vincristine or ATRA were added into culture solution. After 48?h, cell counting kit-8 was used to detect the median inhibitory concentration (IC50) of vincristine combined with ATRT treatment to SO-RB50?cells. SO-RB50?cells were divided into drug combination group, vincristine group, ATRA group and control group. Different drugs were added into the culture solution respectively for cell culture based on the IC50 value. Cell counting kit-8 was used to detect the cell proliferation every 24-h cultivation. After continuous determination for 6?d, data was processed to draw the cell growth curve. After drug use for 72?h, flow cytometry was used to detect the proportion of different cell cycles of SO-RB50?cells in each group. After drug use for 48?h, annexin V/propidium iodide method was used to detect the SO-RB50?cell apoptosis in each group. RESULTS: The IC50 value of vincristine treatment on the SO-RB50?cells was 0.11?μmol/L, and ATRT was 12.84?μmol/L. The cell growth curve in control group rose gradually along with the extended culture time, but after vincristine and ATRA treatment, the cell growth curve was smooth and steady. The cell increment was the least in drug combination group and its cell growth curve was the smoothest. There was significant difference in A450 48?h and 72?h after treatment (Fgrouping?=?77.316, P?