Abstract: Objective To evaluate the effect of ALDH1A1 silence on the proliferation， clone formation and invasion of human gastric cancer cell lines. Methods The siRNA expression vector， PGPU6／GFP／Neo-ALDH1A1，targeting ALDH1A1 were constructed and transfected the gastric cancer cell line MKN-45 cells. The MKN-45 cells were divided into siRNA group（negative group），PGPU6／GFP／Neo-group（experimental group） and blank control group. After transfection， the protein expression of ALDH1A1 was detected by the Western blotting assay. The MTT assay， the colony forming unit assay and the transwell test were performed to detect proliferation， colony forming and invasion of MKN-45 cells through down-regulating expression of ALDH1A1. Results The level of protein expression of ALDH1A1 in experimental group was significantly decreased than negative group（0.36±0.04 vs. 0.72±0.08，P＜0.05）.Compared with negative group， the proliferation inhibitory of MKN-45 cells were obviously increased in experimental group［（52.56±1.81） vs. （30.32±2.23），P＜0.05］； the colony forming unit of MKN-45 cells in experimental group was obviously reduced（21.67±2.00 vs. 36.78±3.53，P＜0.05）； the invasion MKN-45 cells in experimental group was obviously reduced （55.11±7.98 vs. 84.78±6.00，P＜0.05）.Conclusion Down-regulating the expression of ALDH1A1 in gastric cancer cell line MKN-45 by siRNA interference， ALDH1A1 can inhibit the proliferation，colony forming and invasion of human gastric cancer cell MKN-45. ALDH1A1 is a potential target for treating gastric cancer.