The seasonal activity of  Kilifia acuminate (Sign.) on mango trees was studied for two successive years (March, 2011 to mid-February, 2013) in a privet farm cultivated with mango trees at El-Saff, Giza Governorate. The obtained results revealed that, K. acuminata has two overlapping generations on mango trees per year. The 1^st generation (spring generation) started from early March in the both years, peaked in early May and extended to mid-August in the 1^st year and late July in the 2^nd one. The generation duration ranged 5.0 - 5.5 months in the two years at 24.6 - 25.0ºC & 55.3 - 56.2%R.H. The generation size ranged 92.0 - 99.6 nymph/leaf and 69.6 - 79.3 adult/leaf with total population ranged 161.6 - 178.9 insect/leaf in the two years, respectively. The 2^nd generation (autumn generation) occurred between early July and mid-February, peaked in early/mid-October in the both years. The generation duration lasted for 8 months in the two years at 22.3 - 22.6ºC & 659.7 - 60.1%R.H. The generation size ranged 121.4 - 129.7 nymph/leaf and 99.1 - 109.1 adult/leaf with total population ranged 220.5 - 238.8 insect/leaf in the two years, respectively. The insect population recorded with minimum numbers in June, July and early August in the two years.  The population of both nymphs and adult females ranged 63.9-75.2 nymph/leaf and 45.1-71.3 adult/leaf; the total population ranged 109 - 150.4 insect/leaf at 29.4-30.5ºC & 56.1 - 57.1 R.H. %, respectively. The optimum range for insect activity ranged 24.6 - 25.0ºC for spring generation and 22.3 - 22.6ºC for autumn generation. Statistical analysis indicated that the insect population exhibited positive response to the increase of daily mean temperature in both years. The changes in the half monthly counts of nymphs and adult females population referred to the combined effect of daily mean temperature and %R.H. on the spring generation (1^st generation) were 82.1- 82.5% & 73.5 - 82.4% for 1^st and 2^nd year, respectively. The effect of both tested weather on the nymph and adults in the autumn generation (2^nd generation) were 85.1 - 90.9% & 75 - 79.5% for the 1^st and 2^nd year, respectively.