Radioiodine ablation is ineffective in patients with radioiodine nonresponsive thyroid carcinoma. We investigated the effects of all-trans retinoic acid (ATRA) combined with histone deacetylase inhibitor, tributyrin on sodium-iodide symporter (NIS) expression, radioiodine uptake, and inhibition of cell proliferation in a poorly differentiated follicular thyroid carcinoma (FTC-133) in vitro. FTC-133 cells were cultured in the presence of ATRA and tributyrin either as a single agent or in combinations for 48 h. The expression of NIS mRNA and protein was, respectively, detected by quantitative real-time polymerase chain reaction and western blot. The radioiodine uptake was determined after incubation of FTC-133 cells with 125I-iodide. Finally, the cell proliferation test of FTC-133 was performed after treatment. Enhanced expression of NIS mRNA and protein was observed in FTC-133 cells treated with ATRA and tributyrin, which further resulted in significant higher levels of radioiodine uptake than that of untreated control cells and cells treated with ATRA alone. Additive inhibition of the proliferation of FTC-133 cells was also observed with the combination of ATRA and tributyrin. The combination of ATRA and tributyrin induced a synergistic effect on radioiodine uptake and inhibition of FTC-133 cells proliferation in vitro. However, further in-vivo studies and additional molecular research will be needed to determine the absolute efficiency of radioiodine therapy.