Ash agglomerates deposited on the heat exchanger causes slagging and fouling, which decreases efficiency of heat exchanger of boilers. The ash fusion temperature can be important factor of slagging and fouling. This paper presents a prediction model for deformation temperature of woody biomass ash. There are two prediction model: one is quadratic and cubic model using index A by correlation coefficient, and other model is calculated by multiple linear regression using components and indices of previous studies. The coefficients of determination(R2) of quadratic model, cubic model, and multiple linear regression model are 0.835, 0.8367, 0.9175, respectively. Therefore, multiple linear regression model can predict deformation temperature of biomass ash.