The stable nitrogen isotope (δ15N) patterns of soil and leaf decrease with increasing mean annual precipitation (MAP) have been found both in regional and global scale. However, the mechanisms for these patterns are not clear. A potential mechanism is that nitrogen (N) losses relative to pool sizes are greater at drier sites and, because the N lost (via volatilization, denitrification, and leaching) is typically depleted in 15N, this leads to 15N-enrichment of soil and plants in the drier sites. If so, we expect to see that soil available N should be more enriched in 15N in drier sites. The study aims to explore the regional pattern of δ15N of soil available N (0-l0cm) and their relationships with climate along an approximately 3300 km grassland transect in northern China. We hypothesized precipitation was the dominant factor to influence the soil N cycling and δ15N of both nitrate (NO3-) and ammonium (NH4+) should decline with increasing precipitation. Results indicated that δ15N of soil NO3- increased with the MAP increasing at the regions where MAP<200mm. and declined with the MAP increasing at MAP>200mm. The MAP accounted for 46.0% and 3 1.6%of the variation of the 15N of soil NO3- values across the two distinguished regions, respectively. Nitrate concentration displayed a decreased trend with the MAP increasing, and the extremely higher soil NO3- concentration at sites with MAP < l00mm may be caused by atmospheric deposition, which in turn may change the pattern of soil δ15N with MAP. The pattern of δ180 0f soil NO3- with MAP should be applied to confirm the uncertainty. Ammonium concentration initially exhibited increasing and then decreasing trend with MAP at the breakpoint of 200mm. The measurement for δ15N of soil NH4+ is in progress.