Peat is an organic soil which has very low bearing capacity and very high compressibility; its organic content is higher than 75%. Peat is classified into two categories, amorphous granular peat and fibrous peat (fiber content > 20%). Fibrous peat has higher bearing capacity compared to the amorphous one due to its fiber content. When the fiber undergoes decomposition, however, its bearing capacity drops, and bigger compression takes place. For this reason, decomposition process of fibrous peat has to be accelerated before the construction starts in order to prevent the change of its properties. In this study, lignocellulolytic bacteria was used to accelerate the fiber decomposition. The results show that 10% of bacteria with 28 days of curing period had the optimum results. The fiber content decreased from 50% to 36.67% in 28 days of curing period. The coarse and medium sizes of fiber decreased 5.13% and 22.03%, respectively; but the fine fiber increased 27.16% because of the change of coarse and medium fiber. Its unit weight and specific gravity decreased 6.83% and 7.89%, respectively. The peat compression increased 22.95% compared to the initial one; but the internal friction angle decreased 27.29%.