We generated transgenic silkworms that synthesized human type I collagen alpha 1 chain [alpha 1(I) chain] in the middle silk glands and secreted it into cocoons. The initial content of the recombinant alpha 1(I) chain in the cocoons of the transgenic silkworms was 0.8%. The IE1 gene, a trans-activator from the baculovirus, was introduced into the transgenic silkworm to increase the content of the chain. We also generated silkworms homozygous for the transgenes. These manipulations increased the alpha 1(I) chain content to 8.0% (4.24 mg per cocoon). The alpha 1 (I) chain was extracted and purified from the cocoons using a very simple method. The alpha 1(I) chain contained no hydroxyprolines due to the absence of prolyl-hydroxylase activity in the silk glands. Circular dichroism analysis showed that the secondary structure of the alpha 1(I) chain is similar to that of denatured type I collagen, demonstrating the absence of the triple helical structure. Human skin fibroblasts were seeded on the alpha 1(I) chain-coated dishes. The cells attached and spread, although at decreased chain concentrations the spreading rate was lower than that of the collagen and gelatin. Cynomolgus monkey embryonic stem cells cultured on the alpha 1(I) chain-coated dishes maintained an undifferentiated state after 30 passages, and their pluripotency was confirmed by teratoma formation in severe combined immunodeficient mice. These results show that the recombinant human alpha 1 (I) chain is a promising candidate biomaterial as a high-quality and safe gelatin substitute for cell culture. Biotechnol. Bioeng. 2010;106: 860-870. (C) 2010 Wiley Periodicals, Inc.