The purpose of this thesis is to study how the weight reduction has changed water, electrolytes and hormone in Ssirum players. For this experiment, urine and blood of 9 Ssinum players were selected. They were classified as normal condition, 3㎏-reduced condition, 5㎏-reduced condition and recovering condition. Water, electrolytes, and hormone were chemically analyzed and compared. The result is as follows : 1. Urine volume is significantly decreased in weight-reduced condition, and significantly increased in recovering condition. 2. The creatinine of urine is insignificantly shown in weight-reduced condition, but in is significantly decreased in 3㎏-reduced condition and recovering condition, 3. Osmolality concentration, sodium and chloride of urine are significantly changed in reduced condition and recovering condition. 4. The potassium of urine is significantly decreased in 3㎏-reduced condition, but there is on difference in 5㎏-reduced condition. 5. Plasma Anti-Durectic Hormone (ADH) is increased in reduced condition, but there is little significant difference between reduced and recovering conditions. 6. The change of Plasma Renin Activity (PRA) is significantly increased in reduced condition, but it is significantly increased in recovering condition. 7. Water and electrolytes in recovering condition are quickly normalized, but hormone is relatively slowly normalized.