Nowadays, geotechnical specialists are focused on reinforcing soil engineering parameters using innovative and environmentally friendly methods. Microbial-Induced Calcite Precipitation is a ground improvement method for modifying soil strength, permeability, and stiffness; therefore, it can be vital to study the effective factors on the technique’s efficiency and cost reduction. This study examined how biologically treated sands subjected to undrained triaxial loading responded to simultaneous changes in cementation solution molarity, optical density (OD600), and curing time. The triaxial experiments showed that the strength increased with the rise in the mentioned parameters. While the solution molarity and optical density had the highest and lowest effect on the soil improvement process, respectively, the optical density role was considerably low when the molarity was high. Increasing the molarity of the cementation solution resulted in a 45% increase in the peak stress ratio, while the optical density and curing time were constant. On the other hand, similar behaviour of dense sand and change in the response of cemented soil from strain-hardening to strain-softening were other notable observations of this study. In addition, the peak stress ratio at low strains increased with increasing the cementation level and then decreased to close to the amount of untreated sand with increasing strain.