Objective To investigate the effect of senescence-associated secretory phenotype-conditioned medium (SASP-CM) on the proliferation of human gastric cancer cell lines BGC823. Methods BGC823 cells were divided into three groups:SASP-CM group, tumor cells control-conditioned medium (CTR-CM) group, and normal-conditioned medium (NOR-CM) group. BGC823 cells in the SASP-CM group were treated with paclitaxel (PTX) to establish senescent cell model and to prepare SASP-CM. The establishment of senescent cell model was confirmed by senescence-associated β-galactosidase staining. The concentrations of major SASP factors in SASP-CM were detected by enzyme linked immunosorbent assay, the proliferation ability of BGC823 cells was detected by CCK-8 assay and cell clone formation assay, and the cell cycle and apoptosis were detected by flow cytometry. Results After treating BGC823 cells with 35 nmol/L PTX for 72 h, a steady senescence model was established, which had the highest percentage of senescence cells ([66.95±3.54]%). The concentrations of interleukin (IL)-6, IL-8, chemokine (C-X-C motif) ligand 1 (CXCL1), chemokine (C-C motif) ligand 2 (CCL2), and interferon γ (INF-γ) in the SASP-CM were significantly higher than those in the CTR-CM (all P<0.01). The relative clone formation rate of BGC823 cells in the SASP-CM group was significantly higher than those in the CTR-CM group (P<0.01) and NOR-CM group (P<0.05). The proliferation activity of BGC823 cells in the SASP-CM group was significantly higher than that in the CTR-CM and NOR-CM groups after incubation for 48, 72 and 96 h (all P<0.05). The percentage of S phase cells in the SASP-CM group was significantly higher than that in the CTR-CM and NOR-CM groups (both P<0.01), and there was no significant difference in cell apoptosis rate between groups. Conclusion SASP-CM can promote the proliferation of human gastric cancer cell lines BGC823.