Lung cancer is one of the most common malignant tumors in the world. Anti-silencing function 1B (ASF1B) has been demonstrated to play crucial roles in various tumors. However, the function of ASF1B in lung cancer remains to be addressed. Quantitative real-time polymerase chain reaction (qRT-PCR) and western blot assays demonstrated that ASF1B expression was upregulated in human lung cancer tissues and cells. High expression of ASF1B in lung cancer patients was associated with tumor stage and lymph node metastatic status and indicated a poor prognosis. The results of CCK-8 and colony formation assays indicated that ASF1B promoted the proliferation of lung cancer cells. Moreover, ASF1B knockdown suppressed xenograft tumor growth and inhibited the levels of ASF1B and Ki-67. Transwell assay demonstrated that ASF1B promoted the migration and invasion of lung cancer cells. Importantly, mechanism analysis implied that upregulation of ASF1B decreased the expression of P53 and P21 while increasing the expression of Snail and Slug. Consistently, the knockdown of ASF1B led to the opposite results. Notably, P53 activation with Nutlin3 significantly weakened the epithelial-mesenchymal transformation (EMT) promotion effect of ASF1B, while P53 inhibition with pifithrin-α significantly enhanced the EMT promotion effect of sh-ASF1B. These data indicated that ASF1B exerts its oncogene function partially through the P53-mediated EMT signaling pathway. In conclusion, ASF1B promotes cell proliferation, migration, and invasion through modulating the P53-mediated EMT signaling pathway in lung cancer, suggesting that ASF1B may provide a promising target for the therapy of lung cancer.