Morin is a functional flavonoid commonly found in human diet. Compared to being used solely, it is evident that morin can be more effective as a drug adjuvant. However, research on the combined effect and its corresponding mechanism is limited. Here, we found that morin significantly potentiated the inhibitory effects of the natural compound celastrol on the proliferation of lung cancer cells. Morin and celastrol synergistically exhibit marked apoptosis induction in lung cancer cells, accompanied by changes in the abundance of apoptosis-related proteins. Transcriptome analyses revealed that the combination of morin and celastrol had a significant impact on the number of differentially expressed genes in lung cancer cells. Among these genes, BIRC3 was one of the most significantly different ones, which plays a crucial role in the process of tumor resistance to apoptosis. In addition, several genes identified are primarily associated with intracellular signal transduction pathways, specifically the NF-κB signaling pathway. Importantly, the treatment combining morin and celastrol in tumor-bearing mice results in a synergistic effect that significantly suppressed tumor growth. These findings indicate that morin could be a promising functional adjuvant, and the combination of morin and celastrol has potential for the treating lung cancer.