Silk fabric samples were mordanted with alum [KAl(SO4)(2).12H(2)O]. Then, the samples were dyed with cochineal (Dactylopius coccus Costa) and gall oak (Quercus infectoria Olivier) shellac extracts. Optimum dyeing parameters were determined by using different concentrations of these natural colorants. All the dyed samples were cut into two equal pieces. One group of the parts were post-mordanted with FeSO4. A reserved-phase high-performance liquid chromatography (RP-HPLC) with the diode-array detection (DAD) method was utilized for the identification of the components of dyes present in the all dyed and post-mordanted samples. The color coordinates and fastness values of washing, perspiration, rubbing, and light were investigated and compared with each other. Using a mixture of these natural dyes enhanced the exhaustion of the dye and good color fastness test results were achieved.