Oystershell scale, Lepidosaphes ulmi (L.) (Homoptera: Diaspididae) is one of the most common scale insects that attacks olive trees in Egypt. Therefore, the population density fluctuation of L. ulmi and its parasitoids, and their relations to some weather factors were investigated on three olive varieties (Picual, Coratina and Chemlali) at Faculty of Agriculture, Assiut University, Egypt, during 2017/2018 and 2018/2019 seasons. The results indicated that the pest population was concentrated during the period from April to September. The highest average of L. ulmi population was recorded on picual variety (7.81 and 8.96 insect/ 10 leaves) during 2017-2018 and 2018-2019 seasons, respectively. While the lowest population average was recorded on coratina (4.72 and 5.01 insect/ 10 leaves) during 2017-2018 and 2018-2019 seasons, respectively. During both seasons, there were significant differences in the average numbers of L. ulmi among the olive varieties, picual, coratina and chemlali. Theresults also showed that picual variety was more infested than other two varieties. Survey of L. ulmi parasitoids resulted in two species of parasitoids, Aphytis chrysomphali (Mercet) and Aphytis disppidis (Howared). The average percentage of parasitism was relatively high during, May, June, July and August on picual and chemlali varieties. While on coratina variety the average percentage of parasitism was relatively high during, April, May, September, December, and January during 2018-2019 season. Statistical analysis of the data indicates that, no significant differences among the percentage of the average annual parasitism on the three varieties (4.86 % on chemlali, 4.22 % on picual and 3.89 % on coratina variety). The effects of weather factors on the population of L. ulmi and its parasitoids and the effects of these parasitoids on the population of the pest were also studied. The results might be helpful in an IPM program to control the oystershell scale insect, L. ulmi and to settle the best time for pesticide application on olive varieties.