Objective To investigate the expression of miR-21 and PDCD4mRNA in colorectal cancer and their correlation with clinicopathological characteristics,to elucidate relationship between PDCD4and miR-21 in vivo.Methods Expression of RNA (including miR-21and PDCD4mRNA) and PDCD4 protein were detected respectively by quantitative real-time reverse transcriptase-PCR and SP immunohistochemical staining in 43 cases of colorectal carcinoma and corresponding normal mucous membrane tissue.Results In colorectal carcinoma,expression of miR-21 was higher than that of the control ( P ＜ 0.05 ),and expression of PDCD4mRNA lower than the control ( P ＜ 0.05 ).Expression of miR21 was associated with lymph node metastasis and clinical stages ( Ⅰ + Ⅱ,Ⅲ + Ⅳ ) ( P ＜ 0.05 ).On the other hand,no significant differences were observed regarding sex,tumor site,size,local invasion,distant metastases,clinical stages( Ⅰ,Ⅱ ) (P ＞ 0.05 ).Expression of PDCD4mRNA was associated with local invasion,clinical stages ( Ⅰ,Ⅱ ) ( P ＜ 0.05 ).While no significant differences were found concerning sex,site,size,lymph node metastasis,distant metastases,clinical stages( Ⅰ + Ⅱ,Ⅲ + Ⅳ ) ( P ＞ 0.05 ).miR21 levels was negatively correlated with PDCD4 expression including nuclear and nuclear and cytoplasmic put together (P ＜ 0.05 ),in contrast to PDCD4mRNA and PDCD4 expression in cytoplasmic ( P ＞ 0.05 ).Conclusions ( 1 ) Abnormal expression of PDCD4 mRNA and miR-21 correlate with prognosis in colorectal cancer.(2) miR-21 suppress translation of PDCD4mRNA by binding to the 3'-untranslated region (3'-UTR)of target PDCD4mRNA.