Planthopper harbors eukaryotic endosymbionts that are essential for normal development and growth of the host. Our previous studies suggested the possibility that the symbionts play an important role in nitrogen metabolism of the host through utilization of uric acid, a nitrogenous waste product. To examine the precise role of the symbiont, we prepared synthetic diets with various concentrations of amino acids, and measured uric acid contents stored in the insects reared on these diets. The results showed that planthopper synthesizes uric acid not only as a waste product, but also as a storage product when it ingests an excess amount of amino acids. We also investigated effects of the uric acid storage on growth of the normal and symbiont-depleted host. It turned out that in nitrogen deficiency the stored uric acid is consumed by the symbiont in order to sustain the growth of the host. In addition, we noted that the uric acid content of the host egg is highest at oviposition, and decreases significantly with its development, suggesting that the egg is supplied with uric acid by its parent prior to oviposition. These results are reminiscent of the nitrogen recycling reported for cockroaches.