Background Dexamethasone in conjunction with type 3 serotonin receptor antagonists are being used to the prevention and treatment of chemotherapy-induced nausea and vomiting and postoperative nausea and vomiting in clinic. The present study aimed to investigates the stability of ramosetron with dexamethasone in infusions, with the goal of enhancing the safety and clinical applicability of their combined use. Methods Ramosetron hydrochloride (3.0 μg/mL) combining with dexamethasone (0.05, 0.1, 0.2 mg/mL) were prepared with 0.9% sodium chloride injection and then packaged in polyolefin bags or glass bottles. The stability were investigated kept in the dark at refrigeration for 14 days and at room temperature for 48 h. Results The concentration of both drugs maintained at least 97% in the various solutions for both storage conditions with light protection. In the light exposure conditions, as the extension of storage time, the concentration of both drugs had declined. All antiemetic mixture solutions remained clear and no changes in color, turbidity, precipitation, and the pH remained stable. The insoluble particles were in line with Chinese Pharmacopoeia. Conclusion Our findings suggest that combinations of ramosetron hydrochloride with dexamethasone sodium phosphate in 0.9% sodium chloride injection remain stable for 14 days at 4°C and 48 h at 25°C when protected from light.