Experimental and theoretical methods were applied to find and understand the phenomenon of brake squeal noise of the Seoul Metro rolling stock on tracks. Generally, it is well known that brake squeal noise is strongly related to stick and slip between brake pad and disk. In most cases for rolling stock on tracks, trailer cars needed more particular attention through the tests, because they were the major sources of brake noise due to frictional braking. There are two types of rolling stocks in Seoul Metro: chopper and VVVF. Both types of rolling stocks for lines 1 and 3 in the Seoul Metro were used for experimental analyses. To study brake squeal noise under various braking conditions, dynamometer tests were performed at the S&T Brake, Co., which is one of major manufacturers of brake pads for rolling stock on tracks. For measuring brake squeal noise, acoustic tests were performed with a microphone in the Gunja depot. And modal tests for brake parts, which consisted of brake lining, brake lining pad, and back plates, were executed to obtain the natural frequencies related to the brake squeal noise. Also, modal tests of the whole brake assembly and lining block were performed at the heavy maintenance shop of the Gunja depot. The mode analysis using an ANSYS was simulated to determine the relations between the mechanisms of brake squeal noise. As the results of the tests and the simulations, it was found that specific natural frequencies of the brake parts affected squeal noise, and also, the reason to create squeal noise. Finally, improvements for reducing squeal noise were proposed, and applied to lines 2and 3 at Seoul Metro rolling stock on tracks.