The colour fastness of silk fabrics dyed with extracts obtained from the palm kernel shell (PKS) of African oil palm tree was evaluated at first in order to clarify the dyeing characteristics of this dyestuff. It was found in the colour fastness test to washing that the colour of the dyed silk fabric became deeper with the number of washing by basic Marseille soap solution and no fading occurred after up to thirty washings. The sample colour also became darker until 10 h of exposure to artificial sunlight illumination by a simulator and then brightened very gradually to 150 h in the colour fastness test to light. While the colour fastness to rubbing for the dyed fabrics was low under wet conditions, it was high under dry conditions. The PKS extracts contain the component substances which have reducing properties. Such unoxidised dye precursors are adsorbed onto the silk fabrics in the process of the dyeing and are oxidised to be colouring matters during the washing and light irradiation. On the other hand, attempts at colour stabilisation treatments to prevent darkening after dyeing by washing showed that treating the PKS-dyed silk fabric with Na2CO3·1.5H2O2 solution was the most effective. This treatment process oxidises the adsorbed component substances and prevents colour change due to the further oxidation. Furthermore, it was found that the colour of the PKS-dyed silk fabric turned black, very dark brown, brown or brown-close to black by the treatments with FeCl2, CuCl2, AlCl3 or VOSO4 aqueous solution, respectively. These are mordant effects by the metallic ions and post-mordanting was more effective in darkening the colour.