To evaluate the interaction between plants and herbivore insects to nitrogen (N), we performed a field experiment of short-term (2 years) nitrogen fertilization (100kg N ha^-1 y^-1) in large scale (10ha) in a deciduous broad-leaved forest of Tomakomai Experimental Forest (TOEF), Hokkaido in northern Japan. We assessed the response of oak (Quercus crispula) to simulated N deposition and herbivore insects. Simulated N deposition led to enhanced plant growth, leaf traits, and secondary defensive metabolites, cellulose and lignin, in oak. Oak herbivore communities showed the strongest effect by enhanced leaf traits by increasing N, P and decreasing LMA in first year. But species richness and abundance of herbivores were not significantly related to enhanced plant traits by N fertilization in both years. These results indicated that N fertilization affected plant growth and foliar traits, changes in plant traits were not consistently associated with feeding types, galler and miner, but changes in foliar traits accounted for increased herbivore damage and the changed community composition.