Two-dimensional electrophoresis and Matrix-assisted laser desorption ionization-time of flight-time of mass spectrometry were used to detect the differentially expressed proteins in serum of tientsin albinao 2 mice with spontaneous breast cancer, normal tientsin albinao 2 mice and tientsin albinao 1 mice. Only nuclear clusterin (n-CLU) was expressed in tientsin albinao 1. Immunohistochemistry and western blot validated that n-CLU was present in normal tientsin albinao 2 and tientsin albinao 1 mammary epithelium, and secretory clusterin expressed in the cytoplasm of normal tientsin albinao 2 mammary epithelium and spontaneous breast cancer. n-CLU may play an important role in tientsin albinao 2 spontaneous breast cancer initiation and development.