To provide a method of manufacturing a thin rubber member capable of accommodating various-size and manufacturing a thin rubber member having a constant thickness. In the first step, a long rectangular rubber strip having taper portions formed at both end portions in a transverse direction of the long rectangular rubber strip is cut to a predetermined length to thereby form a plurality of segmented rubber strips 36. In the second step, taper portions 36B at both end portions in a transverse direction of the rubber strip 36 are overlapped with one another, and a plurality of the segmented rubber strips 36 is connected to each other in the transverse direction, whereby a rubber sheet 38, the end portions of which are tapered and which has a large area, can be formed. Further, the rubber sheet 38 that can accommodate various sizes can be obtained by changing the length of the segmented rubber strip 36 and the number of connections thereof.