Disclosed are: a compatibilizing agent for a polymer alloy, which can increase the compatibility with a variety of polymers; a polymer alloy using the compatibilizing agent; and master batch for a polymer alloy. Specifically disclosed is a compatibilizing agent which is used for the preparation of a polymer alloy by blending at least one polymer (A) selected from the group consisting of a polyphenylene sulfide, a polyphenylene ether and a polyamide with a polymer (B) of a different type from the polymer (A) at such a ratio that the amount of the polymer (A) blended is the same as or more than that of the polymer (B). The compatibilizing agent comprises a nanosheet-shaped layered titanic acid which is produced by intercalate an organic basic compound between the layers of a layered titanic acid.