Abstract:Soil organic matter plays a key role in global carbon cycling and global climate changing. Relationships between organic matter (SOM) content and soil pH in topsoil of zonal soils of the whole country and six great geographical regions (i.e. Eastern, Southern, Northern, Northeastern, Northwestern and Southwestern China) were studied statistically based on the data of 886 soil profiles of zonal soil types defined during the second national soil survey of China. Results show that SOM content and soil pH varied significantly from one geographical region to another. There was obvious trend that SOM contents decreased with increasing soil pH, showing a significant negative correlation with soil pH ( r = -0.332~-0.530, p < 0.001). Partial correlation between them, with controlled annual mean temperature, annual mean precipitation and altitude, was also significant at 0.01 level (rp= -0.217~-0.322). An exponential equation (SOM = a e b pH, a and b were fit constants) can well describe the relationship between SOM content and soil pH The variance of soil pH is found to contribute 12.2% ~22.9% to the total variance of SOM content in the country and the six geographical regions.