Abstract:The amount of urea-N remained in adult silkworm was 22-36% of the amount applied during the fifth-instar.Recoveries from feces were 25-33%;about 11% was found in the residural mulberry leaves,and 25-30% was not recovered,probably lost in the form of NO or NO2.More than 60% of the urea-N that was absorbed by the silkworm was transported into silkgland.The amount of urea-N remained in silkgland accounted for 15-25% of the applied level.The amount of urea-N in cocoon or silk could be compared with those in silkgland of adult silkworm,indicating that urea-N transported into the silkgland had been transformed to a component of silk fibroin,but the contribution to cocoon and silk fibroin ‘was below 1%.It didn‘t exceed 3% even though the times or the amount of feeding were increased,or the treatment was combined with ure-ase.lt may be concluded that the direct of addition of urea to mulberry silkworm could be negligible.The contribution of urea-N applied on leaves of mulberry tree to output of silkgland,cocoon and silk fibroin also could be negligible.