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Collapse refers to a sudden decrease in the soil volume upon wetting which is attributed to a loss in the strength of the inter-particle bonds. Collapsible soils can be founded in vast areas around the word and subtropical areas of Iran. Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils. For this reason, the collapse behavior of loess soils has been the subject of interest. In this study, stabilization of Semnan loess which is composed of fine sand and silt bonded by weak clay bonds, has been investigated. The loess was mixed with Portland cement in the order of 0.5%, 1%, and 2.5% for and with nano-clay in order of 0.05%, 0.1%, and 0.25%. The specimens were prepared to achieve a dry density of 14 kN/m3 and a water content of 5%. Oedeometer tests were performed to determine the collapse potential according to ASTM D5333 after 7, 14, and 28 days. Results showed that both Portland cement and nano-clay could reduce collapse potential. Improvement performance was significantly dependent on the binder content and curing time. The best improvement performance was observed at low nano-clay content and it was reduced by increasing nano-clay content. Unlike the cement stabilization, treatment process with nano-clay was relatively fast that terminated when soil moisture content was evaporated. In addition, in this study, micromechanical soil behaviors were investigated by scanning electron microscopy (SEM) image of the treated and untreated specimens.