The heparan sulfate 6-O-sulfotransferase 3 (HS6ST3) gene is involved in heparan sulphate and heparin metabolism, and has been reported to be associated with diabetic retinopathy in type 2 diabetes. We hypothesized that HS6ST3 gene polymorphisms might play an important role in obesity and related phenotypes (such as triglycerides). We examined genetic associations of 117 single-nucleotide polymorphisms (SNPs) within the HS6ST3 gene with obesity and triglycerides using two Caucasian samples: the Marshfield sample (1442 obesity cases and 2122 controls), and the Health aging and body composition (Health ABC) sample (305 cases and 1336 controls). Logistic regression analysis of obesity as a binary trait and linear regression analysis of triglycerides as a continuous trait, adjusted for age and sex, were performed using PLINK. Single marker analysis showed that six SNPs in the Marshfield sample and one SNP in the Health ABC sample were associated with obesity $(P \lt 0.05)$. SNP rs535812 revealed a stronger association with obesity in meta-analysis of these two samples $(P = 0.0105)$. The T–A haplotype from rs878950 and rs9525149 revealed significant association with obesity in the Marshfield sample $(P = 0.012)$. Moreover, nine SNPs showed associations with triglycerides in the Marshfield sample $(P \lt 0.05)$ and the best signal was rs1927796 $(P = 0.00858)$. In addition, rs7331762 showed a strong gene × gender interaction $(P = 0.00956)$ for obesity while rs1927796 showed a strong gene × gender interaction $(P = 0.000625)$ for triglycerides in the Marshfield sample. These findings contribute new insights into the pathogenesis of obesity and triglycerides and demonstrate the importance of gender differences in the aetiology.