Semaphorin 3A (Sema3A) has recently been proven to play an essential role in tumorigenesis. Here, the role of Sema3A in ovarian cancer is explored. The prognostic value of Sema3A was evaluated using the Kaplan-Meier plotter database, and stable expression cells were established by the delivery of lentivirus harboring SEMA3A cDNA or shRNA into OVCA433 and SKOV3 cells, respectively. Then CCK-8 assay, colony-formation assay, wound-healing assay, and Transwell assay were utilized to verify the effect of Sema3A on tumorigenesis. Co-cultures of ovarian cancer cells (OVCA433 and SKOV3) with a conditional medium collected from the established cells were further utilized to confirm the function of Sema3A. Then, the RNA-seq assay was adopted to explore the underlying mechanism. The results demonstrated that low expression of Sema3A was predictive of poor overall survival in patients with ovarian cancer. Functional experiments revealed that Sema3A inhibited proliferation, migration, and invasion in ovarian cancer cells. Secreted Sema3A in a conditioned culture medium also exhibited an anti-tumor effect in ovarian cancer cells. RNA-seq assay suggested that focal adhesion and Lin28B were involved in regulating Sema3A. Rescue assays further verified that Lin28B/ROCK1 axis was vital in the regulation of Sema3A and Lin28B significantly upregulated ROCK1 through let-7g microRNA. The presented data indicate that Sema3A inhibits proliferation and metastasis via the downregulation of Lin28B/ROCK1 in ovarian cancer.