Macrosomia or increased fetal size than normal is one of the major clinical problems that carry health hazards for both mother and fetus .Macrosomia has different causes, however mostly associated with mild hyperglycemia or gestational diabetes .In the present study the histological and histochemical structure of back skin with the underlying brown fat was studied in macroscomic fetuses of mildly diabetic rats and compared to control. The main objectives were to correlate structural changes in such organs with the increase in fetal body weight above average normal. Animal care and experimental protocols and procedures were approved by the Institutional Animal Care King Fahed medical research center Jeddah Saudi Arabia. Mild diabetes was induced in female rat prior to pregnancy via intra peritoneal injection of Alloxan in a dose equal to 100 mg/kg body weight) dissolved in citrate buffer .Three days latter blood sugar was checked and animals with blood glucose ranging from 130-250 mg/ ml (mild diabetes) were divided into subgroups ( 4 animals per cage) at day 20 gestation, animals were anaesthetized with ether, abdomen was opened and uterine horn were cut longitudinally. Fetuses with a weight that ranged between (6.5 -6.7 g) were considered macrosomic compared to normal weight fetuses( 3.9 -5.8 gm.). The results showed insignificant increase in the number and thickness of epidermal cell layers, significant increase in dermal thickness mostly due to edema , and increase in surface area occupied by brown fat lobules, Most cells of the latter tissue showed transformation to white type adiopocytes. Histochemistry proved increased lipid accumulation within dermal fibroblasts, scanty accumulation of lipid droplets in epidermal cell layers and significant lipid accumulation in the brown fat adipocytes. Insignificant increase in polysaccharides content was observed in examined tissues. CONCLUSIONS: The present results could be preliminary to demonstrate histological and histochemical changes in cutaneous and adipose brown tissue that may explain the increasing of body weight and size in macrocosmic fetuses of mildly diabetic animals. The results were discussed in view of available literature. Key words : macrosomia – diabetes- histology and histochemistry -inter scapular skin- brown fat body.