1. Changes in urine and blood properties and heart rate (HR) of carp were investigated during and following hypoxia. 2. When carp were exposed to hypoxic conditions, urine flow in some carp increased immediately. However, it decreased gradually with time. Osmotic pressure and Na+, Cl-, Ca2+ and Mg2+ levels in urine increased in contrast to urine flow. K+, P, ammonium, and lactic acid levels in urine increased gradually. 3. When carp lost their balance, blood pH and plasma K+ were lower, and RBC, Ht, Hb, Mg2+, P, ammonium, lactic acid, and glucose in plasma were higher than those of the control. 4. As water-dissolved oxygen level was restored, urine flow increased immediately and soon decreased to the control rate. Other urine properties showed higher values than the initial levels and decreased with time. No significant change was found in urinary protein. 5. The relationship between HR and urine flow is discussed.