The purpose of this study was to determine the effect of all-trans retinoid acid (ATRA) on two nasopharyngeal cancer (NPC) cell lines and to evaluate the synergistic effect of ATRA used in combination with cisplatin, a standard chemotherapeutic agent for NPC. Two NPC cell lines (NPC-TW01 and NPC-TW04) were used, and the MTT assay was used to analyze cell growth inhibition under various concentrations of ATRA and cisplatin. Under low concentrations of ATRA, the growth of both cell lines was significantly inhibited. When ATRA was used in combination with cisplatin, the resulting synergistic effects were robust and significant. Only a low concentration of ATRA was required to produce a synergistic effect when combined with cisplatin, indicating the potential usefulness of a combination therapy regimen. Therefore, the combination of ATRA and cisplatin is a viable treatment option for NPC and should be further investigated.