The use of microbiologically induced calcite cementation for ground improvement presents a new and innovative ground improvement technique for geotechnical engineers. This method may have provide a very effective way for improvementation of soils and prevent liquefaction-induced damage. This technique uses non-pathogenic micro-organisms which are found naturally in a soil structure and could make a cementation base for sand particles. This method does not have some harmful environmental impacts which may occur when conventional ground improwment techniques such cement grouing or chemical grouting are used. This study presents the results of an experimental research that was conducted to investigate the effect of microbiological properties induced calcite cementation in sands. In order to determine the optimum conditions for calcite precipitation at laboratory when a soil microorganism called Sporosarcina Pasteurii (PTCC-1645) is injected into a soil structure, firstly, an systematic laboratory experiments was conducted in liquid phase using some experiment design methods. In this study the values of urea, calcium cloride concentration, pH, temperature and percent of bacteria was considered as experiment variables and the results was statistically analysed to find the optimum conditions. It was shown that the best reaction of bacteria is presented when 0.5 mol of urea and calcium cloride concentration and 9% of bacteria are mixed at 7-9 value of pH in 25 degree temperature. Under optimum condition, Bio-treatment of the sand was performed using Sporosarcina Pasteurii (PTCC-1645). A uniform graded sand was selected as a soil type for this study. Soil samples was compacted in cylindrically shaped pvc columns with 5 cm diameter and 11 cm height to achieved a density of 1.60 gr/cm 3 and the grouting procedure was initialized. Then the bacterial suspension was injected and after 24 hours, cementation solution at constant pressure was added. The treatment procedure was repeated three to four times for five houres to achive a maximum precipitation of calcite. After cementation, the specimens were dried at 70? in a oven. In order to investigate the grouting effects on the soil, the treated specimens were subjected to different mechanical tests such as unconfined compression test on dry samples, permeability test on wet samples,determination of compression pulse velocity for dry samples and unconsolidated-undrained triaxial compression tests after 3, 7, 14 and 28 days. The maximum uniaxial compressive strength was 680KPa at the 28 days and the cohesive and friction angle was determined 110KPa and 41 degree respectivelly. The calculated permeability was also decreased almost one order compared with a not treated sand.