As population grows, more land areas are used up for accommodation, industrial needs as well as infrastructure. This results in diminishing availability of soil with good characteristics that can be used. This limitation forced future construction to be built on soils with poor characteristics. These types of soil require soil improvement in order to make them viable for construction. A relatively new and sustainable improvement method is bio-grouting techniques. The effectiveness of bio-grouting to improve organic sandy silt is studied in this paper. Cylindrical samples with 3.5 cm diameter and 7 cm height are improved by spraying bacteria solution at different solution-to-sample mass ratio and varying proliferation period. The solution-to-sample mass ratio varied from 0.2% – 1%, while the proliferation period is varied to three durations, i.e., 5 days, 13 days, and 21 days. The results showed that the method applied to soil samples could form calcite and obtain an increase in strength. For 5 days and 13 days proliferation period, the optimum solution-to-sample mass ratio is 0.6%, while for 21 days proliferation period, the optimum solution-to-sample ratio is 0,8%. However, for 21 days proliferation period, samples improved with 0.4% and 0.6% shows comparable degree of improvement as 0.8%.