It has been found that cotton is the most comfort giving material found in nature, but for optimizing the cost and other quality parameters, sometimes it is needed to be blended with some synthetic material. Here again to obtain comfort and aesthetic appeal it is dyed with vat dye by varying some parameters like dispersing agent, wetting agent dyeing was carried out and the best result were studied which specified which is the optimum value of the auxiliaries for dyeing this p/c blend. Color strength and fastness properties were measured for the dyed fabrics. In general, the effects on Dyeing of Polyester, Cotton and Polyester/Cotton Blend with vat dye were explored.