In order to develop rural areas sustainably, the senary sector companies related to food and agriculture play important roles. Therefore, the number of such companies have increased recently in Japan. However, one of the challenges for senary sector companies in mountainous areas is to develop value-added products and market as well as to establish the enterprise. This study aims to reveal the process of products and market development utilizing local network of food industries, focusing on the “Kozagawa Yuzu Hirai no Sato” enterprise in Wakayama prefecture, in terms of relationship marketing and value co-creation. An interview survey of the company and people of the local network was conducted to achieve the purpose. As a result, the company develops its own product using other companies’ products as ingredients to enhance the product value and also develops market through the industries’ network thus reducing transaction cost. This shows that networking with members sharing the same values and goals is significant for product and market development of a small senary sector company in mountainous areas.