Expansive soil is one of the problematic soils that has swelling and shrinking behavior due to fluctuations in water content. So far, the potential content of Montmorillonite clay minerals, dry density, and water content are known to be factors that cause swelling potential in expansive soils. The dry and rainy seasons significantly affect soil water content in tropical climates. This study modeled the influence of the tropical climate on the test, namely testing the wetting and drying cycles on tropical residual soils originating from West Java, Indonesia, using a modified oedometer. The specimens are reformed and are compacted at maximum dry density and optimum moisture content based on the Standard Proctor compaction The test results show that the wetting-drying cycle produces a different swelling behavior from the initial swelling conditions. Ultimately, as the wetting-drying cycle progresses, the specimens exhibit a consistent swelling potential of approximately 10% after going through the third cycle, which can be considered as reaching an equilibrium state. The wetting-drying cycle causes the specimen to lose its initial microstructural condition and, at the same time, reorients and rearranges the clay particle sheets. Eventually, microstructural evolution influences the behavior during the wetting-drying cycle through the resulting swelling and shrinkage potential. © 2025 Faculty of Engineering, Universitas Indonesia. All rights reserved.