We developed a mobile phone-based application to judge and record appropriate pesticide use for farmers based on a research project on navigation system for appropriate pesticide uses (Nouyaku-navi). The application, “Nouyaku-navi Goyoboshi-kun”, has been implemented as a Java-based “i-Appli” for FOMA model mobile phones (NTT DoCoMo). The i-Appli executes on a mobile phone, and only accesses the Internet as required, improving the responsiveness of the user interface and minimizing data charges based on packets sent and received. The overall application structure is a client-server system consisting of the client application (CA) for farmers and a server application (SA) to manage master data and pesticide use records. The master data include data of crops, varieties, and pesticide use rules. The master data are set up on the SA before the users can input pesticide use records in the fields with the CA on their mobile phones. The CA only accesses the SA when it needs to receive master data or submit pesticide use records.<br>In cooperation with JA staff and vegetable farmers in Nobeyama, Nagano Prefecture, we conducted an evaluation test on this system to judge and record appropriate pesticide uses, from June to October 2005. The JA staff appreciated being able to access pesticide use records through the SA in order to check when each farmer's fields could be harvested. Some of the farmers who had used the CA said that they did not feel that their own use of it was merited, but that it might be useful for farmers who were inexperienced in pesticide use. And some of them said that the CA was difficult to operate and that they had to modify the estimated harvest date on the CA if growing conditions of their crops varied. The farmers requested the following enhancements to the CA: to display the estimated harvest date and the days before harvest when they input their fields and pesticides, to improve the display of pesticide use records, and to register the pesticides used by each farmer in the master data.