In order to enhance breeding efficiency and meet the needs of breeding experts, an automatic weighing and selection system of individual cocoon and batch measuring in silkworm breeding was developed with Visual Basic 6.0 for Windows. In this system, two electronic balances are controlled through a computer by serial interface and Non-Modem link method. The system achieved the following: firstly, it can automatically collect and calculate data of individual cocoon and batch measuring by MSComm communication control; secondly, based on weighing data, it can automatically discriminate sex through the Bayesian discriminant function and clustering analysis; thirdly, the system provides many methods of individual selection; finally, it is convenient for the query and management of measured data.