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This research shows the results of studies carried out to define and analyze the effect of aging on MSW behavior of Kahrizak Landfill, the biggest landfill in Iran. Studied samples consisted of fresh samples and also aged ones with 5.5, 14 and 21 years of age which were obtained by mechanical excavators in aged burial locations. Analyzing variation in MSW components illustrates that paste fraction of MSW decreases due to aging process while fibers show a rising trend. Also the moisture content and the organic content of MSW reduce below half of the initial values while the degree of decomposition (DOD) increase up to almost 60% after 14 years. These variations over the time are significantly related to the burying methods and environmental condition of burying location. Shear strength behavior of MSW material was analyzed by some CU tests using large scale triaxial apparatus (D=150mm, H=300mm) on remolded MSW specimens. General observations depict that with an increase in strain level, loading rises without any peak point on stress-strain curves. Fresh samples represent the lowest shear strength followed by 21, 14 and 5.5 year-old samples respectively. There is a direct relationship between fiber content and shear strength. Internal friction angle of aged samples decreases in comparison with fresh ones while cohesion has an inverse trend and rises over the time. According to the effect of burying condition on MSW characteristics, it seems that DOD factor is a more appropriate factor than age in order to analyze long-term behavior of MSW.