<p>Mekong Delta is the biggest Delta in Vietnam where distributes different types of soft soil with considerable thickness. Thus, soft soil improvement for engineering purposes in this area is very popular. In which, cement is one of the most common binders for soft soil stabilization. However, many areas in Mekong Delta distribute organic soil and salt-contaminated soil, especially along the coastline. Organic matter and soluble salt in soil are unfavourable for soft soil improvement by cement. Therefore, additives should be used in combination with cement for soil stabilization. In this study, a comparative study on the effect of different additives (lime, gypsum, RoadCem, and sodium silicate) on the unconfined compressive strength of cement-treated soil in Mekong Delta will be investigated. Two types of soil, including organic soil (OH soil) and salt-contaminated soil (MH soil), were used for this investigation. The research results showed that the additives used have significantly improved the strength of organic soil both in strength magnitude and strength development. The optimum contents of additives are 4%, 2%, 1%, and 0.5% for lime, gypsum, RoadCem, and sodium silicate, respectively. In which, sodium silicate is the best additive for the improvement of organic soil (strength increase by 702.0%), followed by the descending orders: RoadCem (547.8%), gypsum (418.2%), and lime (346.0%). The research results also indicate that different from organic soil, the addition of RoadCem additive to cement-stabilized salt-contaminated soil resulted in an insignificant increase in strength.</p>