This study was carried out to identify the optimum dyeing conditions for maximum dye uptake of Prunus yedoensis Matsumura flower extract on silk fabric and to investigate hue/tone characteristics and fastness properties of the dyed fabrics. As results, the flower extract was found to contain flavonoids by FT-IR and to show yellowish shade by UV-vis spectrum. Silk fabric was optimized for maximum dye uptake to five repetitions of dyeing at $80^{circ}C$ for 60 min with an extract concentration of 600% owf in terms of both K/S and color differences. Pre-mordanting was more effective to dye uptake than post-mordanting for all of the mordants used. Un-mordanted and pre-mordanted fabric showed YR(Yellow Red) while most of post-mordanted ones did Y(Yellow). Main tones of dyed fabrics were sf(soft) and lt(light) in the case of unmordanting or Al-mordanting whereas they were d(dull) and g(grayish) by post-mordanting with Cu, Cr, and Fe, respectively. The fastness grades to rub and dry cleaning were reasonably good for most dyeing conditions while those to light were poor. Finally dyeing condition for each hue/tone of the dyed silk with the flower extract was optimized considering fastness properties.