Background: microRNAs (miRNAs) are tiny, noncoding RNAs that regulate gene expression on the posttranscriptional level and this may lead to cancer development. This study aimed to detect the serum levels of microRNA-21 gene expression and to assess their relation to colorectal cancer (CRC) outcome and correlate it with carcinoemberyonic antigen level. Methods:  the collected blood samples from 48 subjects already diagnosed as CRC and 48 healthy controls. A quantitative reverse transcription polymerase chain reaction (qRT-PCR) was using in the measurement of the expression levels of miR-21 .The obtained  data were used to measure the association between serum microRNA-21 levels and clinic pathological and prognostic factors. Results: High serum expression of microRNA-21 have been correlated with greater local recurrence, TNM staging, PT staging, venous invasion, liver metastasis and recurrane (p=0.004), positively correlated with CEA. Conclusions: There was a correlation between the expression level of serum miR-21 and CEA, recurrence and some pathological parameters of patients with CRC. Our results suggest that circulating serum microRNA-21 is a promising tumour marker, can be used in diagnosis and prognosis of CRC.