Abstract: The rock mechanical properties of the limestone samples from the Qum Formation between 2 300 m to 3 300 m in Well Arn-2 and Well Fkh-1,the central Iran Basin have been studied under the simulated formation conditions(including the confining pressure,the temperature,the type of the pore-saturating fluid,and the direction of sampling).The results indicate that the compressional deformation characteristics of the rock samples can be classified into 2 types according to the shape of the stress-strain curves: elastic deformation and elastic-plastic deformation.Almost all samples show brittle failure under the formation conditions,with the total axial pre-failure strain being normally less than 3%,and being mostly about 1%.The change scope of the mechanical parameters of all samples are broad due to the great differences in the burial depth;the compressive strength is 46.52 to 288.31 MPa;and the range of Young's modulus is 11.00 to 286.53 GPa.The compressive strenghty,the Young's modulus and the Poisson's ratio of Member E of the Qum Formation in Well Fkh-1 are all greater than those of Member E of the Qum Formation in Well Arn-2.While within the Qum Formation in Well Fkh-1,the compressive strength is greater in Member A than that in Member C than that in Member E,indicating that the compressive strength increases with depth.The effect of the fluid on the mechanical properties in Well Fkh-1 is as follows: the compressive strength and the Young's modulus of the oil-saturated rocks are greater than the compressive strength and the Young's modulus of the water-simulated rocks respectively.When the weak planes pre-exist in the rocks,the compressive strength and the Young's modulus remarkably decrease.For most samples,the compressive strength and the Young's modulus in the direction parallel to the bedding plane are different to those perpendicular to the bedding plane.