Colourfastness properties of degummed Rajshahi silk (Bombyx moriimproved multi-voltinevariety) were studied as a function of exposure to sunlight in air, washing with soap solution and spottingwith acids and alkalis under different modifying and dyeing conditions. Study showed that 30% aceticacid and 20% tannic acid together was the best modifier for dyeing with Chrysoidine-Y, magenta,brilliant green, Victoria blue-β, Crystal violet and Auramine O basic dyes. Among the dyes, brilliantgreen exhibited best colourfastness under the prolonged exposure to sunlight in air. Washing withsoap solution did not deteriorate colours at room temperature (27◦C), but deterioration was observedwith the increase of temperature. All the dyes used withstood their colours on silk to a great extent onwashing with soap solution, although it slightly decreased with the increase of washing temperature.Spotting with acids and alkalis gave satisfactory results in most cases with the exception for sulphuri