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Background and Objective: MicroRNAs have emerged as post-transcriptional regulators that are critically involved in the biologic behavior of cells. This study was designed to investigate the effect of members of the microRNA-29 family on the expression of cell division cycle 42 (Cdc42) and their roles on proliferation, migration, and invasion of gastric cancer cells. Methods: We detected microRNA-29s and Cdc42 expression in gastric cancer cells by real-time polymerase chain reaction (PCR) and Western blot analysis. Negative controlled RNA (ncontrol), microRNA-29 family members (microRNA-29a, -29b, and -29c), and Cdc42-specific small interfering RNA (si-Cdc42) were chemically synthesized and transfected into SGC7901 and BGC823 gastric cancer cells, which have a relatively low expression of microRNA-29s and a relatively high expression of Cdc42. The expression of Cdc42 and the phosphorylation of its downstream molecular PAK1 expressions were determined by Western bott analysis. Cell Counting Kit-8 was used to measure cell proliferation, and wound-healing and invasion assays were used to examine the abilities of migration and invasion. Results: Similar to si-Cdc42, the ectopic expression of microRNA-29 family members significantly reduced the expression of Cdc42 and its downstream molecular PAK1 phosphorylation levels. Consistently, ectopic expression of microRNA-29s inhibited proliferation and migration in gastric cancer cells. Invasive cell counts of the SGC7901, ncontrol/SGC7901, si-Cdc42/ SGC7901, microRNA-29a/SGC7901, microRNA-29b/SGC7901, and microRNA-29c/SGC7901 cell groups were 84.0 ±4.2, 71.7± 4.6, 16.3 ± 3.2, 15.7 ± 3.8, 16.3 ± 3.0, and 16.7± 3.1, respectively. The invasive cell counts of the BGC823, ncontrol/BGC823, si-Cdc42/BGC823, microRNA-29a/BGC823, microRNA-29b/BGC823, and microRNA-29c/BGC823 cell groups were 199.0 ± 10.5, 146.3 ±9.7, 72.7 ± 8.2, 86.7 ± 8.5, 86.0 ± 8.5, and 73.3 ± 8.3, respectively (P < 0.05). Conclusions: Members of the microRNA-29 family can obviously inhibit cell proliferation, migration, and invasion of gastric cancer cells by targeting Cdc42.