Silkworm is an important industrial insect with many unique characters. Combining ability of parents at animals and silkworm is dependent on different genetic effects that cannot be analyzed completely with phenotype performance. Many reports have showed that many good characters at silkworm have heterotic effects (Rajanna and Puttaraju, 1998). In Sericulture, the parents with high general combining ability are used generally for improvement of silkworm population performance. These parents considering additive effects and additive×additive effects produce high heterosis. Meanwhile the special combining ability includes non-additive effects, dominant effects and other genetic effects (Singh et. al. 1990). Double cocoons have two pupae together in one cocoon. These cocoons are an important section of production by silkworm. Therefore, analysis of combining ability for double cocoon character is beneficial for understanding of its genetic specifications and improvement of production level.