Nutritional incides have important role in economical efficiency of silkworm rearing. In order to estimate nutritional indices six silkworm hybrids including 103×104, 31×32, 107×110, 104×103, 32×31 and 110×107 which were commercially used in Iran for cocoon production were tested. These hybrids were reared in spring 2003, spring 2004 and autumn 2004. The studied parameters were amount of ingestion and facea, digested food, percentage of ingestibility and digestibility, reference ratio (ingested feed/produced feces), larva weight gain, efficiency of conversion of ingested (ECI) and digested (ECD) food into larva weight. The obtained results clearly indicate that ingestion, digestion and utilization of food were mostly dependent upon genotype and hybrid's instars. Hybrids E and F at instars 1-3 and instars 4-5 duration ingested less food. Food ingestion was different at the same season of different years. Meanwhile this index have many alteration upon rearing season. At spring season, the first and third instar larvae obtained the most ingested foods. At autumn season, other instars obtained the most ingested food. Ingested food amount affected by larval duration and also by climatic conditions especially rearing season. Hybrids E and F had the highest digestibility in comparison with other hybrids. Comparisons of common hybrids (A, C and E) against the reciprocal hybrids (B, D and F) for percentage of ingestibility and digestibility is showed Japanese hybrids have nutritional indices higher than Chinese hybrids. But at instars 4-5 these results were reverse i.e. Chinese-maternal based hybrids have nutritional indices higher than Japanese-maternal based hybrids. Obtained results are showed nutritional indices were different in various silkworm hybrids and it must be noticed to hybrid production based on nutritional characteristics.