The present paper presents a cytohistological study of adult mouse ovary by applying trichrome staining techniques and highlighting the main morphological changes which accompany cells in apoptosis, in different types of ovarian follicles. The results obtained by analyzing histological sections of ovarian tissue in adulthood (90 days) show that apoptotic process is active in all types of ovarian follicles, but with different intensity from one follicular stage to another or from one cell type to another, the most critical stage being represented by the transition to preantral follicle stage. From the stage of primordial follicle to that of preantral follicle, a frequent cause of follicular atresia is the oocyte in apoptosis, a process morphologically marked by the appearance of specific nucleo-cytoplasmatic changes. From preantral follicle stage to that of pre-ovulatory one, a frequent cause of atresia is developed by the appearance of morphological changes specific to apoptotic process in granulosa cells firstly and its later expansion in oocyte and then in internal sheath’s cells.