Smartphone is now playing an important role in our daily life. The various sensors and multiple features of smartphones can collect abundant information about people's life experience, which is called mobile life-log. Life-logs are useful for people to recall past meaningful events and remind of meaningful experiences. However, as the amount of life-log becomes vast, it requires an efficient way to organize and store such vast information. Semantic networks, which are used to implement human retrieval system, can help people to effectively organize and retrieve life-logs collected from smartphones. In this paper, we propose a method of mobile life-log search based on semantic relation in semantic networks. By using semantic relation, we reduce the unnecessary intermediate results so as to reduce the usage of computer memory and retrieval time. To demonstrate the usefulness of the proposed method, we constructed mobile life-log semantic networks and conducted experiment on it. As a result, the proposed method is useful for life-log retrieval in the semantic networks.