Abstract: A four-year field trial was carried out to determine effect of nitrogen(N) and potassium(K) combined application on mulberry(Morus atropurpurea Roxb.) during 1999-2002 and a silk worm(Bombyx mori Linne) experiment was conducted to determine their consequential effect on silk cocoon yield and quality in summer of 2001. The results showed that N and K fertilization significantly increased mulberry leaf yield,but the effect of only N without K treatment was very limited and high rate K with low rate N hindered the improvement of leaf yield.In comparison with leaf yield in other treatments,high rate N and K treatment N 450 and K2O 300 kg/(haa) received the highest yield,which increased by 35.2% over N0K0 treatment.Essential amino acids,total amino acid,protein and fat content in leaves were increased by N and K application,indicated that N and K combined fertilization improved mulberry leaf quality.The treatments of only N without K decreased amminoacido metionina and fat content in leaves,while K application decreased sugar content.Silk worms fed results showed the death rate of worms was lower with the N and K fertilization leaves and cocoon weight,cocoon shell percentage and shell yield were increased.The silk cocoon quality test showed that silk worms fed with mulberry leaves from K treatments produced better quality cocoons in terms of silk worm weight,cocoon weight,reelable cocoon rate,filament length,reelability and silk neatness.N application improved cocoon quality combined with K,but had negative effect on quality without K application.The results revealed appropriate N and K management for mulberry orchards had important role on mulberry leaf product and silk cocoon yield and quality.