Materials are limited for pest control and chemical pesticides are prohibited in organic farming. Thus, the concept of pest control may not be effective for pest management in organic farm. As an alternative approach, landscape management is potentially effective and useful approach for preventing pathogen and insect pests in organic farm. It is needed to develop best practices utilizing functional biodiversity for pest management through landscape management. For this purpose, we investigated the effect of companion plants on species richness of insect pests and natural enemies in the field border area and in the crop plants (rice and soybean). In rice paddy fields, Lysimachiae foenum-graecum, Saururus chinensis were selected as effective companion plants on the paddy field levee for conserving Arachnidae as natural enemy and density suppression of insect pest such as Lissorphoptrus oryzophilus, Riptortus clavatus. As a result, damage rate of rice plant by insect pests was significantly lower (2.5%) and yield rate of healthy grains was significantly higher (8.7%) than control. In soybean fields, Marigold plants such as Tagetes patula, T. officinalis, increased Arthropod species richness and ratio of natural enemy group, and decreased ratio of insect pest group. As a result, yield (weight of 100 seeds) of healthy soybean was significantly increased (2.5%) than control. The 2nd infection rate from damage by R. clavatus was significantly lower in the treated plot than that in control. Thus, yield rates of healthy soybean in the control and the companion plant-treated plot were 79.0% and 84.3%, respectively, compared to conventional farming using chemical pesticides. Therefore, use of companion plants on field border was an effective practices for preventing pest insects and increasing yield in organic farming.