Abstract: Ryugyong Hotel in Pyongyang, DPRK, is a 105-storey skyscraper with a high of 323.55m and its foundation mainly consists of fine-grained sandstone, siltstone and silty slate clay. The former involves about 50% of the total formation. A modified borehole jack was used to measure the Young' s modulus of the base rock. Unlike Goodman Jack suggested by ISRM, BJ-110 Borehole Jack gives the true rock modulus directly without any correction. The results show that the elastic modulus of fine-grained sandstone ranges from 6-14GPa, and those of siltstone and silty slate clay about 21GPa and less than 3GPa respectively. The settlement observation was carried out during construction. According to the total weight and the settlements observed, the average calculated modulus of the foundation is about 6GPa, approximately coincidents with the measured one To obtain the average modulus of the foundation before construction, a method will be introduced in this paper.