The study was carried out to investigate the feasibility of chemical mordants on cellulosic fibres (i.e., cotton) dyed with onion peel extract which is an unconventional source of natural dye. The colour value of the dyed samples and also the colour fastness properties with respect to wash, perspiration, crock and light was assessed. The results showed that the dyed samples gave dull pastel shades. The cotton samples dyed in neutral medium exhibited more dye exhaustion and colour variation as compared to the samples dyed in alkaline medium. As far as colour fastness properties are concerned, all the dyed samples showed fairly good results.