In Algeria, few studies seem to have been carried out on olive tree diseases. The present work is a contribution based on field observations and notations as well as symptomatological diagnosis of diseases of fungal, bacterial and insect pest origin affecting the olive tree. Surveys were carried out in olive-growing regions in northern Algeria from February to December 2024. These surveys revealed the presence of eleven diseases, two of fungal origin (verticillium wilt and scab) and one of bacterial origin (olive tuberculosis, Pseudomonas savastanoi).Eight diseases are caused by insect pests: Olive Fly(Dacus oleae), Olive Moth(Otiorhynchus cribricolis), Olive Moth(Prays oleae), Olive Thrips(Liothrips oleae), Neiroun (Phleoetribus Scarabeoides), Olive Psyllid, Jasmine Moth(Margaronia Unionalis) and Olive Black Scale(Saissetia oleae).