Bending of sandwich beams has been treated as a non-linear problem. The non-linearity is called forth by the distributed thrust in the compression face. The non-linear differential equations for cantilevered sandwich beams with concentrated load at end are solved by using load parameter power series. On account of the labour involved in this method, the solution has been calculated up only to terms containing the square of the load. This will be an approximation going a little beyond the usual small load range which can be covered by a linear theory. Its value is not so much that it gives a correction to linear theory, but rather that it shows the latter's range of validity. The results of the present theory show that if the fixed faces are stressed to their elastic limit, they almost always have appreciable non-linear stresses. The theoretical expressions give good experimental checks. The existence of such non-linearities clearly demonstrate that the proposed use of the experimentally determined "composite plate constants" from the linear theory will be of doubtful validity. In the face the linear bending stress of the outmost fibre at the fixed end is found always greater than the linear mean normal stress. Thus treatment of the faces as mere membrances, to simplify the bending problem of the sandwich plate, is likely to lead to large errors.