Paper is aimed to study analytically the steady characteristics of the fully cavitated hydrofoils by acceleration potential concepts. By taking the usual linearized assumptions, the problem can be reduced by Tulin transformation to potential one of mixed boundary type. Basic integral equation with respect to acceleration potential, resulted from the boundary condition over the hydrofoil, is of Sohngen's type. After examining the behaviour of singularity of pressure at the leading edge from the acceleration potential obtained, the lift and drag are expressed in a form of Munk's integral. Then it is shown that the present method of analysis can be easily extend to the fully cavitated hydrofoils with upper and lower free boundary of practically extreme importance.Numerical calculations are made for the fully cavitated hydrofoils with upper free boundary and the effect of upper free boundary on the steady characteristics are examined in some detail. Comparisons with experimental results confirm the present theory as far as the linearized assumptions hold.