Abstarct: One of the most important geotechnical issues that can affect the design of the project or lead to its destruction is the existence of problematic soils. Problematic soils are divergent,expansive, collapsible, liquefied soils. In this research, special attention has been paid to collapsible soils. Various researchers have researched the stabilization and improvement of collapsible soils. In this research, the effect of rice straw waste fibers (RSF) on the mechanical behavior of collapsible soils stabilized with cement has been investigated. Studying of the effect of different percentages of mixing of these fibers on the compressive strength of collapsible soils stabilized with different amounts of cement through performing unconfined compressive strength (UCS) test and evaluation of the effect of the so-called fibers and cement on the results of standard compaction test (SCT) has formed the basis of laboratory research in this project. Results of standard compaction test have shown that as the percentage of fibers in equal cement content increased, the maximum dry unit weight and optimum water content decreased and increased, respectively. The results of unconfined compressive strength test revealed that in specimen containing 1% fibers, the compressive strength increased, by 89.49% compared to the specimen containing 0.25% fibers. In specimens stabilized with the cement and without curring time, the compressive strength increased by 60% compared to the reference specimen (containing 0% fibers and 0% cement) with increasing the amount of cement. Moreover, failure strain decreased by 28.40% compared to the reference specimen (RS). Also, results of uncured specimens containing fibers and cement have shown that in the specimen containing only 1% fibers compressive strength increased by 172.38% with increasing the amount of cement from 0% to 12% and failure strain decreased by 68.10%. It is remarkable that in specimens containing 12% cement and 0.25% fibers, with increasing curing time from 0 days to 28 days, the relative compressive strength increased by 1594%, and relative failure strain decreased by 21.48%. In general, aging and increasing the curing time has increased the relative compressive strength and decreased relative failure strain. In general, the results show that the compressive strength of cemented specimens is higher than reinforced specimens, and the specimens containing fibers failed in more strain than cemented specimens. The results show that in general, in the short term, by replacing the fibers and reducing cement content, the required compressive strength can be obtained and the failure strain can be increased, but in the long term, the effect of the hydration process is dominant to rice straw fiber effect and Reducing the amount of cement only increases the failure strain and decreases the compressive strength.