This paper presents the effect of objective lens tilt on bit error rate (BER) characteristics in magneto-optical disk recorder which is used for non-compressed digital recording at high density and high bit rates. The author studied the relation between coma aberration and optical moment for the Airy ring of the focused spot image. The lens tilt margin was determined by a BER level of 3_??_10^-5 for a bit length of 0.33 μm/bit under the conditions of NA=0.55 and a laser wavelength was of 680nm. The lens tilt margins for a triplet lens and an aspherical lens was within ±0.1 and ±0.2 degrees of angle, respectively.