Background: The study aimed to determine the incidence of K-ras and BRAF mutations in colorectal cancers (CRCs) in Thai patients and evaluate association with clinicopathological parameters including treatment outcomes in terms of event free survival (EFS). Materials and Methods: Two-hundred colorectal cancer specimens were collected for studies of K-Ras codon 12, 13 and 61, and BRAF codon 600 by polymerase chain reaction and direct nucleotide sequencing. Results: The overall incidence of K-Ras mutations in our patients was 23%. K-ras mutation frequencies in CRC stages (AJCC) I, II, III and IV were 6.7%, 16.1%, 23.3% and 26.6%, respectively (p-value>0.05). The three most common mutation forms were G12D, G12V and G13D. K-Ras mutation status was associated with poorer EFS in stage I-III CRCs (p-value 0.03). Conclusions: The study found a lower mutation frequency of K-Ras and BRAF compared to reports involving other ethnic groups. However, K-Ras mutations did have a negative prognostic value in early-stage CRCs.