Experiments were done to investigate the effect of processing conditions on fastness properties of natural dyes on silk fibers. Four types of natural dyes viz. manjista bark, arjun bark, dalim powder and ghabb powder obtained from Indian plants were used. Haritaki solution was used as premordant and aluminium sulphate was used as mordanting agent. Dyeing carried out at neutral pH for 1-2 hours at 100°C gives better results with respect to both light and wash fastness point of view. Premordanting and mordanting is necessary particularly light fastness point of view.