Abstract: The hydraulic fracturing technique is an efficient method for direct determination of in-situ stress in deep (boreholes. This article describes the general principle, technique and instrumentation of hydrofracturing, presents the results of two field hydro-fracturing tests performed in Yisian County, Hebei Province (1980) and Xinyi County, Jiangsu Province (1981) respectively, and gives the magnitudes and directions of the in-situ stresses obtained. The results obtained by hydrofracturing are compared with those by overcoring at the same test sites.