SLD5 is a member of the GINS complex, essential for DNA replication in eukaryotes. It has been reported that SLD5 is involved in early embryogenesis in the mouse, and cell cycle progression and genome integrity in Drosophila. SLD5 may be involved in malignant tumor progression, but its relevance in human cancer has not been determined. Here, we found strong SLD5 expression in both human bladder cancer tissues from patients and cell lines. Knockdown of SLD5 using small interfering RNA resulted in reduction of cell growth both in vitro and an in vivo xenograft model. Moreover, we found that high levels of SLD5 in bladder cancer cells result from downregulation of microRNA (miR)-370 that otherwise suppresses its expression. High level expression of DNA-methyltransferase (DNMT) 1 and IL-6 were also observed in bladder cancer cells. Knockdown of IL-6 led to downregulation of DNMT1 and SLD5 expression, suggesting that IL-6-induced overexpression of DNMT1 suppresses miR-370, resulting in high SLD5 expression. Our findings could contribute to understanding tumorigenic processes and progression of human bladder cancer, whereby inhibition of SLD5 could represent a novel strategy to prevent tumor growth.