Abstract: In order to widening the application domain of monascorubrin, the dyeing of silk with monascorubrin was researched in this paper. The effect of pH, mordant concentration and mordanting method on the dye uptake and K/S was investigated. The washing-fastness and light-fastness of the dyed samples were also researched. The results indicated that the rare earth could form a complexation with the monascorubrin and fiber, which improved the dye uptake and K/S. The washing-fastness of the dyed samples was 4 grades. The light-fastness was 3~4 grades. The optimum dyeing formulation was simuhaneous-mordanting, mordant concentration 1g/L, pH=3, liquor ratio 1：30。