The improvement of water resistance of natural leather is a worldwide subject of investigation in leather industries. The present study was carried out to examine the effects of tanning and retanning agents on the water vapour and liquid water absorbability of collagen fibers as a fundamental study. By a recovery process with a less degree of alkali treatment, collagen fibers were obtained from the shoulder part of salted steer hide (58 lbs.). When the collagen fibers were treated with vegetable tannin or basic chromium sulfate, their absorbability of collagen fibers for the vapour and liquid water decreased as the degree of tanning increased. Such decreases were greater in case of chrome tanning at high pH values. Retanning with syntans and vegetable tannin showed a tendency to increase the vapour and liquid water absorbability of chrome collagen fibers. On the other hand, retanning of chrome collagen fibers with resin type syntans, acrylic resin (emulsion type) and inorganic tanning agent was recognized to cause a reverse effect.