This study was performed in finishing pigs to investigate the effects of betaine HCl on carcass fat deposition and lipid metabolism in relation to growth hormone (GH) and insulin-like growth factor 1 (IGF-1) alterations. Sixty cross-bred finishing pigs (30 gilts and 30 barrows) with an average initial body weight of 74.0±1.8 kg were randomly allocated into two groups, each with six replicate pens. Each group was fed either 0% or 0.125% betaine HCl supplementation for 41 days. Results showed that the betaine HCl supplementation had no effect on growth performance (P> 0.05). In the betaine-supplemented group, Lenden-speck-quotient index, average back fat thickness, serum triglycerides concentrations and fatty acid synthase (FAS) activities were lower than those in the untreated control group (P< 0.05, P< 0.01, P< 0.05 and P< 0.05, respectively). The betaine supplementation did not alter serum GH concentrations (P> 0.05), but serum IGF-1 concentrations were higher in the betaine group (P< 0.01). In conclusion, betaine reduced lipogenesis by reducing the FAS activity and increased serum IGF-1, leading to improvement in carcass characteristics.