Parthenogenetic development, hybrid vigour and cocoon shape variability were studied in bivoltine F1 hybrids of the silkworm, Bombyx mori L. Considerable breed differences were observed in parthenogenetic ability. Among the parental breeds, CSR18 exhibited maximum parthenogenetic development (79.65%) followed by CSR4 (67.90%). Among bivoltine F1 hybrids, CSR18 ${ imes}$ CSR4 showed highest parthenogenetic development (73.32%) followed by CSR2 ${ imes}$ CSR4 (55.43%). Study on hybrid vigour demonstrated that CSR18 ${ imes}$ CSR19 expressed maximum significant hybrid vigour for all the seven economic characters over Mid Parent Value (MPV) followed by CSR2 ${ imes}$ CSR4 and CSR18 ${ imes}$ CSR4 exhibiting significant heterosis for six characters. Cocoon shape measurement study revealed that among ten bivoltine F1 hybrids, cocoons of three hybrids were found comparatively uniform. Importance of this study to know the level of paythenogenetic development, hybrid vigour and cocoon shape variability in different bivoltine F1 hybrids have been discussed.