saltColorAmmoniaa b s t r a c tThis research is aimed to study the influence of ammonia after-treatment on color behavior in wool yarnsdyed with annatto extract. The dyeing was carried out using 15% (o. w. f.) dye concentration in presenceof stannous chloride as a mordant and then treated with different percentages of ammonia solution. Atthe same time, color strength, CIE-Lab values and fastness properties of all dyed woolen yarns were alsoassessed. It was concluded that, in all cases after treatment with ammonia caused a decrease in lightness(L*) values, there was less lightness in the red hue of the wool yarns with the increase of ammoniapercentage in solution. The K/S value of annatto dyed wool was found to increase after treated withammonia. In addition, it was also observed that dyed wool yarns after post-treatment with ammonia didnot return to their original color on acidification