Some important aspects in the modelling of enhanced biological phosphate removal processes which are not considered in IAWQ Activated Sludge Model No. 2 are discussed and three submodels are proposed. When denitrification by polyphosphate accumulating organisms (PAOs) is introduced to the model, anoxic uptake of soluble orthophosphate, which is sometimes observed in the real world can be expressed. Appropriate values of stoichiometric and kinetic coefficients remain to be determined. Glycogen storage capability is another essential character of PAOs. By incorporating biochemical information obtained so far, the processes relating to glycogen storage can be modelled. The model implies very delicate kinetic characteristics of PAOs. A group of organisms, which can cause deterioration of phosphate removal and has been referred to as “G bacterium”, is characterized as glycogen accumulating non-poly-P organisms (GAOs). A preliminary model for GAO metabolism is proposed.