The study was undertaken to explore the use of natural mordants on cotton fibres with an unconventional natural substance i.e., onion peel as dyeing material. Dye was extracted from onion peel in aqueous medium and dyeing was done in neutral and alkaline medium. Pre and post mordanting techniques were adopted at room temperature. All the dyed samples were evaluated for their colour value and colour fastness properties. According to results obtained, it was found that dyeing in neutral medium gave the better results in terms of dye absorption and brightness as compared to the samples dyed in alkaline medium. Samples showed good to excellent colour fastness properties against washing, perspiration, crocking and light fastness.