Ultisols are acidic, highly weathered soils with inherently low fertility, commonly found in tropical regions. This study aims to evaluate changes in several chemical properties of Ultisols before and after flooded rice cultivation. Soil samples were collected from five districts in South Kalimantan, Indonesia (Tapin, Banjar, Tanah Laut, Tanah Bumbu, and Kotabaru) and analyzed through a greenhouse experiment using a Completely Randomized Design (CRD) with five replications per location. The observed parameters included pH, total nitrogen (N-total), available phosphorus (P), organic carbon (C-organic), exchangeable aluminum (Al-dd), cation exchange capacity (CEC), and soluble iron (Fe). The results showed that soil pH decreased significantly, while Al-dd increased significantly after rice cultivation. The significant decline in pH is likely attributed to nitrification processes and the accumulation of H? ions during flooding drying cycles. Meanwhile, the significant increase in Al-dd is closely related to the lower pH, which enhances the solubility and release of exchangeable aluminum from soil colloids. In contrast, N-total, available P, C-organic, CEC, and soluble Fe-exhibited changes that were not statistically significant, indicating that these parameters did not undergo substantial alteration. The non-significant responses may be associated with the high variability among sampling locations and the complex chemical and biological interactions occurring under flooded conditions. This study demonstrates that rice cultivation on Ultisols alters specific soil chemical properties, particularly soil acidity and aluminum solubility. Therefore, integrated soil management strategies such as liming, organic matter application, and balanced fertilization are essential to maintain soil fertility and ensure sustainable rice production on Ultisol soils.