We developed and evaluated a Mobile System "Pocket Plant Guide" for supporting the observation of plants. While previous systems used photographs, the "Pocket Plant Guide" uses sketches, which is one of its defining characteristics. This guide contains three types of display as follows; (1) color display of leaves and fruits; (2) display of enlarged leaves and fruits; and (3) display of the underside of the leaves. As a result of an evaluation targeting sixth grade elementary school children, the "Pocket Plant Guide" was quite easy to use and was effective in promoting the observation and understanding of plants.