Background: Secretomes have been gaining interest in treating several diseases due to their pharmaceutical effects, such as the immunomodulatory effect. This study aimed to determine the immunomodulatory effect of secretomes derived from human umbilical cord mesenchymal stem cells (MSCs) and their safety. Methods: We conducted an in vivo immunomodulatory study using a carbon clearance assay. The safety of single-dose administration of secretome was done using fixed-dose methods of acute toxicity test. Results: The phagocytic index was higher in mice treated with secretome than in untreated mice. The acute toxicity study also showed that the administration of secretome derived from human umbilical cord MSCs did not change the mice’s body weight, physical examination results, organ weight, and gross anatomy examination. Conclusions: This study presents the potential of secretome derived from MSCs as a safe immunomodulatory agent.