This research aims to study the effect of mordantson the color values and durability of yarn dyed from the Yang bark, pretreatment with a solution of calcium hydroxide. The copper sulphate and ferrous sulphate were used as mordants.The study found that color values, L *, a * and b * of cotton yarn were all positive. The cotton yarns used copper sulfate had more color values than ferroussulfate.The cotton yarns used copper sulfate were brown hue. andgrayish black hue for ferrous sulphate. . The maximum L * was 61.61 from the 1%CuSO4. 5H2O with post - mordanting, the maximum a * was 8.21 from 0.25% CuSO4. 5H2O with pre-mordanting, and the maximum b * was 20.09 from the 1% CuSO4. 5H2O with pre– mordanting.The color fastness test on washing and sunlight in gray-scale found that pretreatment of cotton yarn with 4% Ca per cotton yarn weight 0.25% copper sulfate as simultaneous mordanting was the best quality in good-excellent durability was 4.50.