This study was carried-out at Orman Garden, Horticulture Research Institute, A.R.C. Giza, Egypt during the two successive seasons of 2013 and 2014. In this study, we aimed to test the effect of different exposure time from microwave on increasing vegetative growth and chemical constituents in Acacia farnesiana and Acacia saligna seedlings. The seeds have been exposed to the microwave radiation for 0s (control), 5s, 10s, 15s, 20s and 25s in the Acacia farnesiana and seeds have been exposed to the microwave radiation for 0s (control), 10s, 20s, 30s, 40s and 50s in the Acacia saligna in the both seasons respectively. Seedlings were planted individually in 30 cm diameter plastic pots filled with 8 kg of mixture of clay and sand at the ratio of (1:1) by volume. The obtained results revealed that the exposure time from microwave showed that significantly increasing in vegetative growth and chemical constituents. From the obtained results, it could be concluded that the highest mean in Acacia farnesiana plant was scored as a result of exposure time at 5 second. Whereas, it could be concluded that the highest mean in Acacia saligna plant was scored as a result of exposure time at 10 second in the both seasons, respectively.