This study aims to explore the influence of fragile X retardation 1 (FMR1) gene knockout on biological characteristics of C57BL/6 (Mus musculus domesticus) mice. Blood physiological and biochemical indexes of FMR1 knockout mice and C57BL/6 mice of 8﹣10 weeks old were respectively examined using animal automatic blood cell analyzer and automatic biochemical detection. The comparison of difference between groups was analyzed with independent-samples T test method using SPSS 19.0. The blood routine indexes of C57BL/6 FMR1 KO male and female mice, such as neutrophilic granulocyte (MEUT#), neutrophilic granulocyte percentage (MEUT) and lymphocyte percentage (LY), had significant difference compared to C57BL/6 mice (P < 0.05); for males, the number of red blood cells (RBC), hamoglobin (HGB), hematocrit value (HCT) and mean corpuscular hemoglobin concentration (MCHC) showed significant difference compared to C57BL/6 mice (P < 0.05); for females, the number of white blood cells (WBC) and lymphocytes (LY#) showed significant difference compared to C57BL/6 mice (P < 0.05); the non-sex factors including red blood cells (RBC), hematocrit value (HCT), neutrophilic granulocytes (MEUT#), neutrophilic granulocyte percentage (MEUT) and lymphocyte percentage (LY) showed significant difference compared to C57BL/6 mice (P < 0.05). But there was no significant difference in the number of platelets (PLT), mean platelet volume (MPV), plateletcrit (PCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), red blood cell distribution width-standard deviation (RDW-SD), red blood cell distribution width-coefficient of variance (RDW-CV), platelet distribution width (PDW), platelet-large cell rate (P-LCR), monocytes (MONO #), monocytes percentage (MONO), eosnophils (EO#), eosnophils percentage (EO), basophilic granulocytes (BASO#) and basophilic granulocyte percentage (BASO) between C57BL/6 FMR1 KO mice and C57BL/6 mice (P > 0.05) (Table 1). Serum biochemical indexes of C57BL/6 FMR1 KO mice, such as the AST/ALT (AS/AL) in males had significant difference compared to C57BL/6 mice (P < 0.05); the creatinine (CR), creatine phosphokinase (CK) and electrolyte Ca2+ in females had significant difference compared to C57BL/6 mice (P < 0.05); the non-sex factors including AST/ALT (AS/AL), creatinine (CR) and creatine phosphokinase (CK) had significant difference compared to C57BL/6 mice (P < 0.05). No significant difference was found in albumin (ALB), globulin (GLB), ALB/GLB (A/G), alkaline phosphatase (ALP), glutamyltransferase (GGT), total protein (TPROT), alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN), uric acid (UA), cholesterol (CHO), triglyceride (TG), glucose (GLU), lactic dehydrogenase (LDH), osmotic pressure, K+, Na+, Cl￣, Mg2+ and P3+ (P > 0.05) (Table 2). Thus, the results suggest that FMR1 gene knockout can influence some blood physiological and serum biochemical values in mice. These results will provide the experimental basis for researching and using C57BL/6 FMR1 KO mouse model in the future.