The present study was carried out in Matrouh Governorate during two successive years (February, 2017- February, 2019) to investigate the population density, population age structure, number of generations, seasonal variation and effect of three weather factors (temperature, relative humidity and wind speed)  onolive black scale, S. oleae infesting olive trees under irrigation system. Results concerning the fortnightly variations of the total monthly counted individuals of S. oleae /5 trees throughout the period of study revealed the presence of six variation periods in two successive years, three in spring months and three in summer months. Considering the population age structure, the immature stage was 83.3 % in 15^th February, , decreased to the minimum of 54.4% of total count in 15^th September,  then the population was increased to constitute a large ratio during autumn and winter months in the first and second growing seasons. The adult females population started with 11.5 % of the total counted individuals in the first season, increased or/and decreased in the next months to reach the maximum of 23.3% in 1^st September, then decreased in autumn and winter months. In the second season, the population took the same trend with slight difference in numbers. The gravid female population was more or less higher in March to July in both two growing seasons. The black olive scale has two generations/year according to the immature stage appearance. The first peak of immature stage individuals was recoded in June and the second in August. The seasonal variations in population densities can be ascendingly arranged as, winter, autumn, spring and summer months. The assessed simple correlation values of three weather factors (daily mean temperature, relative humidity and wind speed) with total count of S. oleae individuals were calculated. Temperature was found to have a positive significant effect on the population, while the relative humidity had an insignificant effect. Wind speed had a positive effect on population density of the olive black scale,(S. oleae).