Objective To investigate the effects of circular RNA APLP2(circAPLP2)on the proliferation,migra-tion,and invasion of human colorectal cancer(CRC)cell lines by regulating microRNA-455-3p(miR-455-3p)/Stathmin1(STMN1)axis.Methods RT-qPCR was used to detect the expression of circAPLP2,miR-455-3p and STMN1 in CRC and normal colorectal cell lines and the optimal cell line was screened.Proliferation,migra-tion and invasion were detected by MTT assay,scratch assay and Transwell assay,respectively.The relationship between circAPLP2 and miR-455-3p,between miR-455-3p and STMN1 was confirmed by dual Lucifer's reporter gene assay.Results CircAPLP2 and STMN1 were highly expressed in CRC cells,miR-455-3p showed a low ex-pression.Knocking down circAPLP2 resulted in a decrease in rate of survival and of scratch healing rate and in-vasion of SW620 cells,An up regulation of miR-455-3p expression,a down regulation of STMN1,cyclin D1,N-cadherin protein expression and an up regulation of E-cadherin protein expression were also found(P<0.05).Inhibition of miR-455-3p expression reversed inhibitory effect of knocking down circAPLP2 on SW620 cell prolif-eration,migration,and invasion,up-regulated the STMN1,cyclin D1 and N-cadherin protein expression,and down-regulation of E-cadherin protein expression(P<0.05).Dual luciferase reporter gene assay showed that circAPLP2 targeted at negative regulation of miR-455-3p expression,while miR-455-3p targeted at negative reg-ulation of STMN1 expression.Nude mouse transplantation experiment found that knocking down circAPLP2 affect-ed the growth of transplanted tumors,while miR-455-3p expression was up-regulated and STMN1 expression was down-regulated(P<0.05).Conclusions CircAPLP2 inhibits the proliferation,migration and invasion of colorectal cancer cell lines by regulating the miR-455-3p/STMN1 axis.