The dyeing of woolen yarn with eggplant peel, a natural colorant, has been studied. The main coloring component in this natural colorant is anthocyanin, which is an interesting class of dyes in the blue and red area. Eight mordants including alum, copper sulfate, ferrous sulfate, potash alum, nickel chloride, zinc sulfate, tin chloride, and potassium dichromate were used for mordanting the fibers. Four different mordanting procedures, pre-mordanting, simultaneous mordanting, a combination of pre and simultaneous mordanting and post-mordanting were used for study the effect of the mordanting procedure on color properties. Various acids such as acetic, chloric, citric, formic, lactic, nitric, oxalic, sulfuric, and tartaric were used to investigate the role of acids in dyeing. Different shades of greenish yellow to semi-blue were obtained from the dye extracted from eggplant peel. Tin chloride as a mordant produced the noticeable semi-blue color. The chromaticity values showed that sulfuric acid resulted in better navy blue hue compared to other acids for mordanted woolen yarn with tin chloride. The combination of pre and the simultaneous (or meta) mordanting procedure was found to be the efficient route for dyeing wool yarn with eggplant peel.