OBJECTIVES: Main goal is to study the BAT (brown adipose tissue) during fetal development of Mongolians by morphometric indicator of structure.  METHODS: Study implementation is followed by guideline was approved by the Statement of Ministry of Health in 16.08.2007 № 223 Appendix №4 and study is also ruled by common methods of morphometric study such as measurement of Bunak.V.V, Avdantilov.G.G and histological method is used to study the examination of tissue and issue. Study involved 30 fetuses and morphometric measurement of  period, length, width and thick are done and 60 units of BAT are assessed by micro preparation. BAT was got from the aborted infants when they are 12 weeks aborted by doctors’ instruction and those are measured and specialty of blood cell is done by inflowing, specialty of cell is done by general and particular method of tissue examination, locality is done by dissection.  RESULTS: BAT is covered thin pellicle and fawn-coloured, when see it, it will different from common WAT and BAT is seen in the armpit, necks and between plate bones, ribs, back of sternums, aorta and top glands of kidney. Main part of BAT is in armpit, muscle serrates anterior and between muscle subscapular. CONCLUSIONS:

1. BAT are located through the ways of aorta and its major branches. However the main mass of the BAT are found between muscle serrates anterior and muscle subscapular.
2. Our results reported that BAT were formed as morphological tissues at 15th weeks of fetal gestation period. Fetal body sizes and morphometric units of BAT are directly and strongly correlated with each other.