Although short-cycle Acacia plantation has caused negative impacts on the mountainous soil environment, the understanding of these impacts is still unknown in Vietnam. Therefore, this study evaluated the effects of short-cycle Acacia plantation on soil properties under successive seven-year cycles in some areas of Vietnam. A total of 182 soil samples randomly stratified by the Acacia cycles were collected at the topsoil depth of 30 cm to analyse the effects of Acacia cycles on changes in the soil properties. Non-parametric Kruskal-Wallis & Mann-Whitney tests were used to assess the differences in soil properties under different Acacia cycles and natural forest. Then, the Analytical Hierarchy Process (AHP) was applied to combine the soil properties into the soil quality index for assessing soil quality in the different cycles. The results showed that changes in the soil properties among the Acacia cycles and the natural forest were statistically different (p<0.05). The AHP-based soil quality assessment shows clearly the varying levels of soil deterioration in the successive cycles. It was also found that the indicators of OM, TN, and pH were more closely correlated with the SQI; therefore, soil conservation measures are indispensable for the Acacia soils. The study is a practical contribution to the understanding of soil quality change in short-cycle Acacia plantation areas that are common in many parts of the world, especially in the tropics.