The objective of this study was to examine the effect of plasma leptin and insulin concentrations on fat traits in Hanwoo. If a biological indicator such as plasma leptin and insulin was identified, it would be a useful biological marker that can be predicted marbling score in young animal. The relationship between plasma hormone (leptin and insulin) and fat traits (marbling score, back fat thickness and P8 fat thickness) was investigated. The experiment studies 100 Hanwoo that were randomly sampled from Hanwoo Experimental Station Herd. The concentration of plasma insulin was significantly associated with marbling score (P=0.02) but was not significantly with back fat thickness (P=0.07) and P8 fat thickness (P=0.09). Statistical model determinant that plasma insulin concentration account for phenotypes was moderate on marbling score (5%), back fat thickness (3%) and P8 fat thickness (9%). On the other hand, plasma leptin concentration was significantly associated with marbling score (P=0.03) and back fat thickness (P=0.02), but was not significant on P8 fat thickness (0.07). Statistical model determinant that plasma leptin concentration accounting for phenotypes was moderate effect on marbling score (3%) and back fat thickness (2%), but it has a slightly bigger effect on P8 fat thickness (7%). In conclusion, the plasma leptin and insulin seems to have an effect on fat traits (marbling score, backfat thickness and P8 fat thickness) in Hanwoo.