At any time, soil will have characterizing compaction strength as a result of its composition, internal processes such as age-hardening and previous external compressive pressure like loaded-wheel traffic. Soil strength is measured in terms of the maximum pressure or “stress” that can be applied before the occurrence of the substantial increase in soil compression. This soil strength is termed “pre-compaction stress value” in much of the literature. One of the natural characteristics of the soils in arid and semi-arid regions is soils with high lime (calcium carbonate) percentage. No information on the effect of lime and age-hardening on compaction strength of calcareous soils have been reported. Therefore, the objectives of this research were to study the effects of lime percentage and age-hardening on soil compaction (pre-compaction stress) and shear strength. In this research, a clay soil with very low lime content was used. Then, soils with different lime percentages (10, 20, 30, 40, and 50) were prepared. In order the soils to regain their natural structure; the soils were kept at field capacity for two months. Experiments were conducted at two gravimetric water contents: 21% and 27% dry basis. Tests on soil were done in two time intervals, immediately and one week after soil sample preparation. The soil in each pot was preloaded by putting load on the soil surface with a 250-mm diameter plate for thirty minute. Preloading stress was 100 kPa. Experiments were conducted on the preloaded soil pot by compression loading with a CBR soil plate penetrometer for the semi-confined plate sinkage tests (PST) and by confined uniaxial tests on soil cores. The effects of lime, water content and time of loading on soil pre-compaction stress and shear strength were studied using a factorial experiment in a Randomized Complete Block Design with three replications. The result showed that, the effects of lime and water content on soil pre-compaction stress were significant at 1% and 5% levels, respectively, but the period of time (one week) in which the soil was kept at a specific water content had no significant effect on pre-compaction stress. For immediate loading and at both water contents, soil pre-compaction stress and shear strength calculated at pre-compaction point, were increased significantly by increasing the percentage of the lime (calcium carbonate) added to the soil. By increasing the percentage of lime added to the soil, the coefficient of internal friction was significantly increased. However, the lime did not have any significant effect on cohesion. The relationship between the pre-compaction stress in two methods, CCT and PST, were linear and high significant (P 0.01). The estimated pre-compaction stresses in both of methods were over-estimated. The pre-compaction stresses obtained with PST were higher than those with CCT. Higher esti