Development and web growth of Atypus karschi were investigated by means of individual rearings under semi-outdoor conditions. Males required 3 years for development from egg to adulthood, passing through 8-9 molts after emerging from the maternal web. Females also developed to adults in 3-4 years with a variable post-emergent molt number from 9 to 11. The mean web width increased from 2.3mm to 13.3mm in males and 13.7mm in females during the period of nymphal development. In the case of adult females, however, web width continued to grow up to 15.9mm or more, since they lived for 3 or more years and repeated a post-adult molt every year. From the examination of seasonal change in weekly excretion frequencies through one year, it was observed that adults and nymphs were still active even in winter. The life cycle of this species is described based on these results and field observations.