Various factors are considered to be mechanisms of the increase in the sizes of cysts in patients with polycystic kidney disease. Vasopressin is one of the causes, and drinking large volumes of water shows an effect of suppressing an increase in cysts. On the other hand, it is known that hydrogen-rich water reduces oxidative stress and has a good effect on kidney injury. We examined whether drinking large volumes of hydrogen-rich water affected the increase in the sizes of cysts. Forty 5-week-old PCK rats were randomly assigned to four groups: C(Control), purified water; W(Water), water with sugar; H(Hydrogen), hydrogen-rich water; WH(Water+Hydrogen), hydrogen-rich water with sugar. They consumed water from 5 to 15 weeks of age. The intake of water in the groups in which sugar was added to the water (W, WH) significantly increased in comparison to C, but there was no significant change in the serum Creatinine concentration. The kidney weight per body weight in W was significantly decreased in comparison to C. The kidney weights in H and WH were significantly increased in comparison to W. There were no significant differences in the ratio of the cross-sectional area of the cysts to the whole area among the groups. This experiment showed that the effect of drinking large volumes of hydrogen-rich water was not significantly different from that of normal water, in terms of preventing an increase in the size of cysts in PCK rats. However, some papers acknowledge the influence of hydrogen water. Significant differences might become obvious if we change aspects such as the administration method or administration period.