Several soil improvement techniques are successfully implemented today. Studies are increasingly becoming popular on microbially induced calcite precipitation (MICP) as an environment-friendly and sustainable method that is an alternative to other soil improvement techniques. Our study examined the effects of different sources of calcium on an improvement that was carried out on a sand soil with a 35% relative density by using the MICP method. The results were analyzed by using unconfined compression, permeability, calcite formation percentage, pH, SEM (scanning electron microscopy) and XRD (x-ray diffraction) experiments. As a result of the unconfined compression test, the strength values were obtained as 2406 kPa in the specimens where calcium chloride was used as a calcium source, 2435 kPa in the specimens where calcium nitrate was used and 64 kPa in the specimens where calcium acetate was used. The permeability experiment revealed a decrease in permeability of 80.8% for calcium chloride, 23% for calcium nitrate and 90.4% for calcium acetate. According to the results of the SEM analyses, the structures that formed in all specimens bound the grains to each other and coated the surfaces of the grains. In the XRD analyses, calcite formation was observed in the specimens where calcium chloride and calcium nitrate were used as the source, while, in contrast, vaterite formations were also observed in the specimens where calcium acetate was used as the source. It was determined that different sources of calcium had different effects on improvement of sand soils by microbially induced calcite precipitation (MICP).