To evaluate the effect of winter intensive training on pulmonary function in high school baseball players, comparisons of various ventilatory parameters were made before and 3-3.5 months of winter intensive tranining. The subjects were 18 members of a high school baseball players with mean age and career of 6.3 and 7.3 years, respectively. The following were mainly observed by spirometry for the study ; respiratory rate, vital capacity(VC), maximum voluntary ventilation(MVV), forced vital capacity (FEV1%) and forced mid-expiratory flow (FEF25-75%). The result obtained are summarized as follow. 1) Resipratory rate, tidal volume, forced vital capacity, 1FEV%, FEF50% and FEF75% showed no significant difference between before and after. 2) MVV in after was significantly(p<0.001) increased to 166 L/min comparing with 136L/min in before. 3) 1FEV in after was significantly(p<0.05) increased to 4.46L comparing with 3.76L in before. 4) PEF in after was significantly(p<0.05) increased to 10.40 L/sec comparing with 9.18 L/sec in before.