Air and soil contamination in developing countries exacerbates due to poor management of waste collection and serves as a morbidity and mortality factor. This study aimed to conduct an assessment of soil pollution level in Ulaanbaatar and establish а correlation between microbial contamination and registered occurrences of contagious diarrheal diseases among children (0-5 years old). This is a cross-sectional study conducted in Ulaanbaatar in June-September of 2016. Samples of soil and contagious diarrheal disease morbidity data in 0-5-year-old children were used. Samples were taken from the sites three times, in July, August, and September. The data analysis was done in the SPSS-21 program and relevant parametric and non-parametric tests were used. The highest level microorganisms were found in the samples taken from sites near major markets and then in the samples from ger areas. The analysis of the samples revealed that 111.78 microorganisms exceed the standard level 1.1 times in summer. The Escherichia coli (E.Coli) and Proteus also contaminated the ground water. All diarrhea occasions in Ulaanbaatar were analyzed by seasons and months, the prevalence was peaking in August. A correlation was found with the soil E.Coli titers and infectious diarrheal disease children under five years old morbidity. The number of microorganisms in soil tends to increase in summer. Diarrheal disease infections among children under five increase most in summer and autumn and correlate with soil contamination with pathogenic microorganisms.