The Purpose or this study was to determine the optimal dyeing condition or Chelidonium majus extracts onto silk fabrics. Among the various dyeing properties, the colorfastness of fabrics dyed with Chelidonium majus extracts was investigated in different conditions such as dyeing temperature, dyeing time, dyeing pH etc. We also tried to dye fabrics using the Chelidonium majus extracts which were lyophilized. Although mordant was not used, dyed fabrics showed relatively good dyeability and the main pigment of Chelidonium majus showed yellow vividly in the appropriate dyeing conditions. At a dyeing temperature above 40$^{circ}C$, the $Delta$E value increased but the yellowish tint decreased. The pH value of unadjusted Chelidonium majus extracts was 6.4, at which a deep yellow was obtained. The dye equilibrium was reached 40 minutes after dyeing. The colorfastness to washing and light was poor at 1-2 and 2-3, respectively, but the dry-cleaning fastness was good at 4-5.