This field experiment was carried out to determine the effect of the third cutting time (July 15 and Aug. 2) and cutting height (3, 6 and 9㎝) at the third cut on the regrowth and summer depression of grasses during mid-summer season. In this study, the grass growth and summer depression index were analyzed in association with temperature and rainfall, and this experiment was done at Livestock Experiment Station in Suwon during 1984-1986. The results obtained are summarized as follows: 1. Ary matter production during mid-summer season was significantly (P$lt;0.05) increased with higher cutting height at the third cutting, regardless of cutting time. 2. The grass growth and summer depression index mostly depended on temperature after the third cutting, The summer depression index of grasses in 1984, 1985 and 1986 were 1.34, 1.83 and 1,51, respectively. 3. The summer depression index was significantly (P$lt;0.05) decreased with higher cutting height. The index observed were 1.89 (3㎝), 1.50 (6㎝) and 1.19 (9㎝) in the plot of July 15, and 2.54 (3㎝), 1.67 (6㎝) and 1.29 (9㎝) in the plot of Aug. 2, respectively. 4. From the results of regrowth of grasses and summer depression index after the third cut, it is suggested that the 9㎝ of cutting height is the most effective during the mid-summer season, regardless of year and cutting time.