Abstract: Objective：To compare the KRAS mutation of primary and liver metastasis tumors and explore the prognostic impact of KRAS mutation in patients underwent simultaneous resection for synchronous colorectal liver metastases (SCRLMs) that were initially resectable. Methods：Clinicopathological and outcome data of 139 consecutive patients with SCRLMs underwent simultaneous resection were collected. The KRAS genotype was evaluated in the primary cancer and liver metastasis tissues by Pyrosequencing. The prognostic value of KRAS status was assessed by KaplanMeier and Cox regression analyses. Results：The perioperative mortality was 0%, and the incidence of complications was 28.1%. KRAS mutated in 28.8% of the primary tumors of the SCRLMs patients, but the genotypes did not significantly associate with any clinicopathological characteristics. There was a high degree of consistency in KRAS mutation rates between primary (29.5%, 28/95) and metastatic lesions (31.6%, 30/95; P=0.157). KaplanMeier survival analysis showed that KRAS mutation was not significantly associated with overall survival (OS), but was significantly correlated with short diseasefree survival (DFS, P=0.041). Multivariate survival analysis showed that KRAS mutation was an independent negative prognostic factor for DFS (P=0.012). Conclusions：KRAS mutation rate is highly consistent in primary and metastatic lesions, and correlated with DFS, so KRAS status should be taken into account when determining concurrent surgical decisions.