<p> A rotary press-in pile with wings has advantages to get large vertical bearing capacity for its pile diameter and to reduce the amount of soil excavated for its installation. On the other hand, it has been concerned that the rotary pile might cause weakening of the soil around the rotary pile. In the case of clay, the authors confirmed the ground around the pile with wings becomes density increase, stiffness decrease and gap occurrence by a past experiment. But, the influence of shape of pile with wings（D_w/D_p）and repeated loading on lateral loading behavior of pile with wings has not been confirmed. In this paper, a series of experiments was performed to grasp the behavior of a rotary press-in pile horizontally loaded, and the property changes of surrounding soil by installing a rotary press-in pile with wings.</p><p> In the experiments, the execution of pile installation was managed with constantly maintaining the ratio of s/p below 1.0, where's is the penetration length of pile rotated by one revolution and p is the helical pitch of it's pile wing. The experiments were carried out at site with a diluvial loam layer. In the experiments, in order to investigate the properties of soil around a pile. We observed the state that the ground around the pile was expanded, after installing the pile. The lateral loading tests, apparatus of one of which was directly equipped with pile shaft and the other of which was normal test, were carried out. In order to investigate the lateral loading behavior, horizontal loading test of the pile was carried out. In order to compare the differences in the pile installation methods, the lateral loading tests for the pile installed by rotation method and the buried pile were carried out.</p><p> </p><p> As a result of this study, the conclusions are as follows.</p><p> </p><p> 1) The coefficient of horizontal subgrade reaction for the rotary pile with wings decreased as D_w / D_p increased</p><p> </p><p> 2)It was confirmed that as the number of times of repeated loading became larger, the coefficient of horizontal subgrade reaction of the pile with wings and straight-pile decreased.</p>