Microbially Induced Calcite Precipitation (MICP) is extensively studied as an environmentally friendly soil improvement technique. The process of bio-cementation of the soil by microorganisms is present in the natural environment. It might be induced by ureolytic bacteria present in soil. In nature this process is slow, but since it is known how it goes, it can be accelerated. The study aims to present how bio-mineralization by MICP method affects the geotechnical properties of fly ash. In the presence of the Urease enzyme produced by the Sporosarcina pasteurii bacteria strain, urea hydrolysis occurs, so CaCO3 is precipitated as calcite crystals and bonds to grains or fulfil the material pores. The ureolytic bacteria are needed for the process of MICP as well as calcium ions Ca2+ present in the cementation solution. In this paper, laboratory test results of Unconfined Compressive Strength of Class F fly ash samples improved by the MICP method are presented and the process of sample preparation is described and discussed.