A RPS (Renewable Portfolio Standard) for South Korea became effective in 2012 with a beginning renewable electricity quota of 2% of total generation of capacities exceeding 500 MW, increasing to 10% by 2022. However, almost of all the coal-fired power plant are not designed to co-firing large amount of biomass with coal. In practice, the biomass cofiring rate is commonly 5 -10% of total heat input. In the case of biomass import, it will cost a great deal on the transshipment, transportation and storage of biomass. Therefore new research and development on the biomass fuel with high energy density in needed to reduce logistics cost on transportation of the biomass fuel. Torrefaction is a thermochemical treatment process of biomass at temperatures ranging between 200 and 300oC. During this process, 70% of the mass is retained as a solid product, and retain 90% of the initial energy content. The physical and chemical properties of torrefied biomass are similar to those of coal. Therefore co-firing torrefied biomass could increase the co-firing percentages much further to even 40%. This review paper looks into the torrefaction technologies of biomass, the technical characteristic of torrefaction reactors, the overview of torrefaction project and the future prospects of torrefaction.