INTRODUCTION:According to the report from 2010, Mongolian water consumption was 550 million cubic meter andapproximately 9.1% of the total Mongolian population obtain their water from inadequate hygiene waterresources - springs and rivers. Due to non-hygiene water usage has caused water-born communicableand non communicable diseases among the population. In the last years there has been issue of pollutionof one of the Mongolia’s more representative river Selenge and its following rivers -Kharaa, Orkhon andit is necessary to evaluate water pollution of these rivers.GOAL:To determine water chemical and biological pollution of Kharaa and Orkhon river and to evaluate waterqualityMaterials and MethodsWe collected water, sediments and macro invertebrates sample from three points of river -upstream,midstream, downstream and for Kharaa river the samples were collected from Tunkhel, Mandal andBayangol soum, fo Orkhon river the sequence was Orkhontuul, Orkhon, Khushaat soum. Samples werecollected June, August, October of 2011, 2013.In water sample, we determined physic-chemical 15 parameters including temperature, pH, total dissolvedsolids, conductivity, smell, color, hardness, sulfate, chloride, nitrate, nitrite, ammonia, dissolved oxygen,biological oxygen demand and mercury using their standard methods. Macro invertebrate samples werecollected to evaluate water quality and we determined mercury in sediments and macroinvertebratesamples to evaluate mercury contamination.RESULT:Physic-chemical results of the water showed that water of Kharaa, Orkhon rivers were classified lowmineralized, soft water and nutrient pollution indicators for ‘slightly polluted’category. For dissolved andbiochemical oxygen, they were belong to the category of ‘pure water’.There were no correlation between 2012 and 2013 results and mercury in water, sediments and macroinvertebrates were qualified standard value.CONCLUSION:According to research results water quality of Kharaa, Orkhon river was good and have less pollution andit is possible to use in household consumption after proper cleaning and disinfection.