To develop vertical jumping ability, some scientists have claimed that free jumping is more effective than weight training (squatting) and that the combination of free jumping and weight training is most effective. In this study, high school students were involved in special training programs (hereafter referred to as "suspension training"), an idea borrowed from speed assisted training (tow training) in running. This training involved the students vertical jumping with all their might while they were pulled upward by rubber ropes attached to their hip belts. Twenty male volleyball players (Age: average SD=15.75}0.72 years) were divided into 3 groups. The first group was involved in free jumping, the second and the third groups were involved in suspension training with an upward pulling force of 10% and 20% of their body weights respectively. They jumped 10 times a day with 30 second rests between the jumps, 3 days a week for 10 weeks in addition to their regular volleyball training. After 10 weeks of training, the vertical jumping ability of the first group increased 3.43 0.50 cm (4.94 0.71%), the second group 7.88 2.47 cm (12.69 7.05%), and the third group 9.60 3.01 cm (15.35 4.56%), respectively. The difference between the average increment in vertical jumping distance of the free jumping group and that of the suspension training group was statistically significant (p 0.001). Differences in the results between the 10% assisted group and the 20% assisted group were insignificant, however.