For the purpose of identifying the effect of body mass index on bone mineral density, an investigation was made in regard to the relationship between body mass index (BMI), bone mineral density (BMD) and bone mineral content (BMC) of lumbar vertebrals of men without osteoporosis. 838 male patients were diagnosed and treated in West China Hospital of Sichuan University because of ostealgia and arthralgia from Aug. 2003 to Dec. 2005. They were examined by dual-energy X-ray absorptiometry, their L2-L4 bone mineral density being < -2.5SD. Then they were graded by body mass index (Kg/m2) [1st group BMI > or =23, 454 cases (Group A BMI > or = 29, 46 cases; Group B 25 < or = BMI < 28.9, 201 cases; Group C 23 < or = BMI < 24, 9193 cases); 2nd group 18.5 < BMI < 22.9, 311 cases; 3rd group BMI < or = 18.5, 68 cases]. The relationships between BMI and BMD of lumbar spine were analyzed using SPSS 13.0. The results revealed their positions in series: (1) Among Groups 1-3, BMD, average BMD and aBMC of L2-L4 being 3rd group > 2nd group > 1st group, the differencs are statistically significant (P < 0.05 or P < 0.01); BMC, aBMC of L3 and L4 and aBMC of L2 being 3rd group > 2nd group > 2nd group, the differences are significant (P < 0.01); besides BMC of L2 and T-score,the differencs among three groups are not statistically significant (P > 0.05); (2) Among the 1st group, BMD and average BMD of L2-L4 being Group C > Group B > Group A,the differencs are significant (P < 0.05 or P < 0.01); BMC, aBMC of L and I being Group C > Group B > Group A,the differences among the three groups are significant (P < 0.05 or P < 0.01); BMC, aBMC of L3 and L4 and aBMC of L2 being Group C > Group B > Group A, the differences are significant, besides BMC of L2 and T-score,the differences among three groups are not significant (P > 0.05), (3) BMI correlated negatively (P < 0.01, r = -0.189) to the average BMD of lumbar spine. The average BMD of lumbar spine decreases when BMI increases in males without osteoporosis. When obesity is more obvious, the decrease in average BMD of lumbar spine bone is more evidently decreased. The decrease of BMD, BMC and total BMC in L3 and L may be greater than that in L2.