Abstract Background First-degree relatives of patients with diabetes (FDR) tend to have impaired insulin activity, which lead to the alternation of circulating cytokine levels. Liver is a main target tissue of insulin action; therefore, liver fat content (LFC) has a close relationship with insulin resistance. This study aimed to find the alteration in serum osteocalcin levels in FDR and the relationship of serum osteocalcin levels with FDR and non-alcoholic fatty liver disease (NAFLD). Methods In total, 1206 subjects including 413 men and 793 women from the communities, aged 59.7 (range, 54.8–64.3) years, were enrolled. An electrochemiluminescence immunoassay was performed to measure the levels of serum osteocalcin. LFC was measured using quantitative ultrasonography. Results A significant decrease was found in serum osteocalcin levels in subjects with NAFLD (P < 0.001) as well as in FDR (19.8 ± 5.7 ng/mL versus 20.7 ± 6.8 ng/mL, P = 0.028). Furthermore, among the subjects with NAFLD, those with FDR had lower levels of osteocalcin than those without FDR (P = 0.011). The presence of FDR remained a predictor for decreased serum osteocalcin levels after adjusting for body mass index, blood glucose, blood lipids, and LFC (standardized β = − 0.057, P = 0.028). Conclusions FDR had lower serum osteocalcin levels than non-FDR. The inverse association between FDR and serum osteocalcin levels was independent of metabolic factors.