Abstract: This paper examines the engineering properties of lime-modified red sandstone residual soil, and determines the best dosage. It takes the red sandstone residual soil in Enshi, Hubei province as a case. It prepares the modified soil samples with different lime contents, and carries out compaction, compression, unconfined compression tests. The results show that, as the lime content increases, the optimum water content of modified soil gradually increases, the maximum dry density gradually decreases, the compression modulus of modified soil decreases first and then increases, the compressive modulus increases first and then decreases. The corresponding optimum lime content is 7%. The unconfined compressive strength of the modified soil increases first and then decreases, the optimum lime content is 9%. The main reasons for above results are that the hydration, ion exchange, carbonation and crystallization of lime can enhance the bonding of sand particles, and improve the integrity of the soil, thus, improves the compression and strength characteristics of the lime-modified soil. However, too much lime can appeare as free-ash between the gap of soil particles, which can lead to deformation increase and unconfined compressive strength decrease of the lime-modified soil.