This paper describes an investigation into influence of the lengths of the slits and the number of those on squeal. In a disk with four slits at regular intervals there are two 2-0 modes which have two nodal diameters. One has a node in the center of a slit (sine mode), and the other has a node between two adjacent slits (cosine mode). The difference Δf1 between the natural frequency of the sine mode and that of the cosine mode becomes greater as the slits grow longer. On the other hand, there is only one natural frequency of the 3-0 mode in the disk. Our squeal theory predicts that the second mode squal is reduced as theΔf1 of 2-0 modes grows greater. Experimental results show that the second mode squeal disappears and the third one is generated when the slits are long. In conclusion, four slits are effective on the second mode squeal, but not on the third one. And also the n-th mode squeal is not generated when theΔf1 of n-0 modes is large.