An optical method for form measurement of cylinder guide bearing is presented. We studied case when all points of guide rolling lay in one plane and generatrix is orthogonal this plane. The method is based on measurement of the cylinder linear speed rolling on the plane guide. Dependence of the cylinder radius on a rotation angle is measured. Possibility of small deviations measurement (an order of several microns) of the guide bearing form from round is shown. A profile of the cylinder with the maximum deviation from a circle ~ 10 microns is obtained. The form of cylinder from roller bearing 3ГП 3 (2Н 102605) was measured. It was shown, that its guide bearing form, measured from mass center, approximately sinusoidal. In can not be found by simply cylinder diameter measuring. The method can be used for diagnostics of the round objects form in the mechanics (wheels, bearings etc.).