background: Our country’s aging for men of 30-39, 40-49 ages it was accelerated aging process and very accelerated aging process. Aging for men of 50-59, 60- 69 ages it was normal aging and slowed aging process. Aging for women 30-39, 40-49 ages it was normal end slowed aging process. Aging for women 50-59, 60-69 ages it was slowed and significantly slowed aging process. Otherwise, aging for young groups was accelerated and very accelerated aging process, aging for old groups was normal, slowed and significantly slowed aging process. The aging process of men was more quickly than women in our country [1].Aim of the stady: To define biological aging, aging indexes and adaptation potential in population of 18- 25 years old of Ulaanbaatar city.Materials and methods: In total 537 person of 18- 25 years from Ulaanbaatar city were chosen for the research study which was conducted in 2012. Biological age levels were assessed on the basis of following standards. True biological age was determined with clinical-physiologycal indexes and biological age with chronological age. Adaptation potential have been studied with the help of special indexes and analysis were made with the use of regression method. Quantative data of the study has been processed with the use of statistical data processing software SPSS- 19.Results and discussions: Body mass index of 18-25 aged men of Ulaanbaatar city was 22.2146, cachexia 7.82%, normal weight 79.32%, more weight 10.24%, obesity 2.6%, Aging for men of 18-25 ages it was significantly slowed aging process of men was observed 0.37%, slowed aging process 0.55%, normal aging 0.93%, accelerated aging process 12.47%, and very accelerated aging process was 85.66%. The portion of men with normal adaptation potential was 55.67%, adaptation functional tension was 43.76%, unsatisfactory adaptation was 0.55%.Conciusions:1. The portion of cachexia 7.82%, more weight 10.24%, obesity 2.6% of 18-25 aged men of Ulaanbaatar city.2. Health status was abnormal 98.13% of 18-25 aged men of Ulaanbaatar city.3. The portion of 18-25 aged men of Ulaanbaatar city adaptation functional tension 43.76%, unsatisfactory adaptation was 0.55%.References:1. 1 .Tuul M., Lhagva L., Sukhbaatar Ts., AmgalanbaatarD. “Aging biology of Mongolians” III book. “Admon” puplisher. Ulaanbaatar. 2009.2. Open society forum. “Policy of young” abstract. UB. 2010.3. Leonid Kalichman, Ida Malkin, Gregory Livshigts, Oleg Pavlovsky, Valery Bathvich. Variation of Skeletal Biomarkers of biological Aging in a Chuvashian Population: A Longitudinal Stady. American journal of human biology 19:74-81. 2007.4. Apanacenco G.L, Popava L.A, “Medical Valeology”. Kiev. 2000.