Metformin has been available 40 years ago. It is used in treatment of type 2 diabetes. Metformin is being used in the management of women with polycystic ovary syndrome and to loose weight. It passes across the placenta and found in breast milk. Therefore, the present work was designed to study the changes in the histological characteristics of structure and ultrastructure of the testes of albino rats due to metformin exposure in utero and during lactation. Fifty-two male offsprings were used in this study. They were divided into four groups. Group 1- It included thirteen male offsprings that were sacrificed one week after birth. Three served as a control group-1 and ten served as a treated group-1. Group 2- It included thirteen male offsprings that were sacrificed after weaning. Three served as a control group-2 and ten served as a treated group-2. Group 3- It included thirteen male offsprings that were sacrificed one month after weaning. Three served as a control group-3 and ten served as a treated group-3. Group 4- It included thirteen male offsprings that were sacrificed three months after birth. Three as a control group-4 and ten male served as a treated group-4. The testicular specimens were subjected to transmission electron microscopic and light microscopic study using Hx. and E., PAS, Mallory's tirchrome and toluidine blue stains. Occasionally, in the same sample, altered seminiferous cords and tubules were found adjacent to normal ones. Thick tunicae albuginea. The testicular blood vessels showed dilatation and congestion. vacuolated and apoptotic spermatogenic cells were noticed with partial separation and distortion of spermatogonia from basal lamina. Also there was vacuolization of some Sertoli cells. Proliferation of the peritubular myoid cells were observed. Some Leydig cells were showed vacuolated mitochondria with distorted cristae. Some myoid cells with many cytoplasmic processes were present. Deposition of material between seminiferous tubules was found. Referring to vacuolation, apoptotic changes, separation of spermatogenic cells from basal lamina and deposition of material between seminiferous tubules were less obvious in treated group-4 and there were stratification of seminiferous epithelium from spermatogonia to sperm like control group. From the previous detections, it could be assumed that the recovery from the metformin effect could occur.