This study is aimed to explore the effect of Judo contestant's rapid weight reductions on their physiological, biochemistry value and motor capacities. Subjects were 7 Judo players participated "2003 National Zhongzheng Cup Judo Championships Tournament". Their average age range, height range, training period range, overweigh range were 21.14±1.34 years, 162.57±4.28 cm. 64.14±8.88 kg, 3.71±1.11 years, 5.29±0.75 kg respectively. All players were determined their blood, urine biochemical value, max, oxygen uptake, max, heart rate and motor capacities before weight reduction. The same determinations had been done to observe the effect of players on physiological condition and motor capacities. The results after weight reduction showed: 1. Urine proteins and blood urea content were both increased (p<0.05), hemoglobin and max, blood lactate content decreased (p<0.05). 2. The max, oxygen uptake and max, heart rate decreased no obviously (p>0.05). 3. The variation of motor capacities: Nage-Waza frequency of players increased (p<0.05) within one minute. Conclusions of the study are that the rapid weight reductions of players effects their urine protein, blood urea content, hemoglobin biochemistry value and max, blood lactate state significantly (p<0.05). On the impact of motor capacities, Nage-Waza of players frequency increases (p<0.05) within one minute.