The increase of anthropogenic nitrogen (N) has increased the amount of N input to forests. This is also causing imbalances in N compared to other nutrients, especially phosphorus (P). This imbalance may potentially have negative effects on growth. The hybrid larch F₁ (F₁) is a promising afforestation species in the East Asian region. To investigate effects of different N and P conditions, N was set in 3 levels and P was set in 2 levels. Fine roots were measured with core samples, and the whole root system was dug out at the end. Needle nutrient condition, seedling growth and biomass was measured. As a result, effects of different N and P conditions were not detected from core sampling. However, from total harvest, fine root biomass increased with N loading at only low P conditions, and fine root proportion to total dry biomass decreased with N loading at both P conditions. Concerning aboveground growth and biomass, there were no differences between P conditions. Therefore, the effect of N loading may differ according to P conditions, indicating the importance of considering both N and P and also, above and belowground growth.