Sand liquefaction refers to a phenomenon whereby sand loses its strength and stiffness. It is responsible for many of the damages associated with earthquake. Partial desaturation of soil using bacterial production of biogas is a new method for mitigation of sand liquefaction. However, there is a concern that whether biogas in sand can be stable over a long duration when there is groundwater flow. In this study, a new method that combines biogas generation in situ with biosealing of the biogas bubbles in sand using a small quantity of biocement was developed. Biogas bubbles were produced in the form of nitrogen gas during microbial denitrication process by denitrifying bacteria Acidovorax sp. DN1 in fully saturated sand. It was experimentally observed of complete removal of biogas under flow conditions with a hydraulic gradient of 0.1 within three days. On the other hand, if sand with biogas bubbles was biosealed with calcium carbonate crystals produced by urease-producing bacteria Sporosarcina pasteurii DSMZ 33, the stability of biogas bubbles was improved by 40% - 70%. Therefore, the sequential biogas production in saturated sand and biosealing of the gas bubbles in sand pores could be useful for sustainable mitigation of sand liquefaction under groundwater flow. The cost of the sequential biogas production in saturated sand and biosealing of biogas bubbles in sand pores could be significantly lower than the cost of biocementation of the saturated sand.