It is well understood that Inter-industry knowledge diffusion has become very significant in knowledge society where innovation based on interdisciplinary is always encouraged. To understand how significant inter-industry knowledge diffusion is, this study classify USPTO patents granted between 1976 to 2013 into five industries, i.e. Chemistry, Mechanical Engineering, Electrical Engineering, Instruments and Other, investigate knowledge diffusion among industries through patent citation analysis. Also, knowledge diffusion is characterized by Number of Claim, Number of Patent Citation Received, Number of Patent Reference, Number of Non-Patent Reference, and Number of Foreign Reference. It is observed that Patents cited by Mechanical Industry and Mechanical patents have Less Number of Non-Patent Reference, and Number of Claim. The results obtained in this study provide a possible way for valuing knowledge diffusion.