In order to determine the effect of dehydration and hydration to the leaf chafer Potosia brevitarsis Lewis, the beetles were measured the change of body water by weighting body mass during dehydration and hydrations including supplying distilled water, salt and sugar under constant 30℃. At the same time, the water loss of leaf chafer was compared with carabid and tenebrionid. The results indicate that the rates of water loss of leaf chafer P. brevitarsis were close to tenebrionid, whose rates of water loss were low. The rates of water loss of leaf chafer and tenebrionid were about 5%, and that of carabid were about 20%, within 10 h. After supplying water, the water of body was increased rapidly. The rates of water loss for dehydration were about 34%, and for supplyingdistilled water, salt, sugar were 28%, 27%, 21%, respectively. And supplying distilled water and salt have no difference with dehydration, while supplying sugar significantly differed with dehydration. The LT₅₀ of dehydrate and upplying distilled water, salt, sugar were 9, 12, 13 and 17 d. Supplying sugar could prolong the life of leaf chafer effectively. So sugar could increase the body water of P. brevitarsis effectively, and play an important role in water balance.