Background: Colorectal Cancer (CRC) is the third common cancer in the world. One of the pathways in colorectal tumor genesis is Microsatellite Instability (MSI+). MSI is detected in about 15% of all colorectal cancers. Colorectal tumors with MSI have dis-tinctive features compared with Microsatellite Stable (MSS) tumors. Due to the high percentage of MSI+ in patients with CRC in Iran, screening of this type of CRC is im-perative. In current study, two markers (BAT-26 and BAT-25) were used to determine an appropriate screening technique with high sensitivity and specificity to diagnose MSI status in patients with CRC. Methods: Allelic variation in two markers (BAT-26 and BAT-25) was analyzed in tis-sues and sera of 44 normal volunteers and tumor and matched normal mucosal tissues as well as sera of 44 patients with sporadic colorectal cancer by Real Time PCR (Hy-bridization probe) and High-Performance Liquid Chromatography (HPLC) techniques. The sensitivity and specificity of Real Time PCR and HPLC compared with sequencing as gold standard. The data were statistically analyzed using Student’s t-test and 2 or fisher exact test, where applicable with (P<0.05). Receiver-operating-characteristic (ROC) curves were used to evaluate the sensitivity and specificity. Results: The sensitivity and specificity of BAT-26 with Real Time PCR method (Hy-bridization probe) were 100% in comparison with gold standard method. Whereas the sensitivity and specificity of BAT-26 and BAT-25 with HPLC were 83%, 100% and 50%, 97%, respectively. Neither HPLC nor Real time PCR could detect circulating DNA with MSI property in sera. Conclusion: The sensitivity and specificity of real time PCR in MSI detection is the same as sequencing method and more than HPLC. BAT-26 marker is more sensitive than BAT-25 and MSI detection with Real time PCR could be considered as an accu-rate method to diagnose MSI in CRC tissues not sera.