Previous in vitro studies have demonstrated that LAG1 longevity assurance homolog 2 (LASS2) is a novel tumor suppressor gene that is significantly associated with the proliferation and invasion ability of tumor cells. However, the role LASS2 serves in regulating bladder cancer cell tumorigenicity and tumor growth in vivo has not yet been elucidated in animal or clinical studies. In the present study, LASS2 knockdown in human bladder cancer EJ-M3 cells significantly promoted the growth of xenografts in nude mice compared with the control group, while overexpression of LASS2 suppressed tumor growth; however, this was not statistically significant. Furthermore, LASS2 knockdown resulted in more apparent heteromorphism and a higher activity of matrix metalloproteinase (MMP)-2 and MMP-9 in xenograft tumors. The data from the present study demonstrated that LASS2 knockdown significantly promoted the tumorigenicity and growth of EJ-M3 xenograft tumors in nude mice, and that LASS2 overexpression has a tendency to inhibit the growth of xenografts, suggesting that it may be a potential therapeutic target for bladder cancer.