Expansive agents are used to reduce cracking caused by drying shrinkage in concrete structures such as slabs, beams, columns and pavement constructions. It also utilised in specific situations such as water leakage prevention in water retaining structures such as water tank, dam, etc. Although CaO and Sulphoaluminate based expansive cement have been used for decades, MgO-based expansive agents have demonstrated superior performance since 1970, especially for concrete dam structures. While other expansive agents have some disadvantages such as poor thermal stability and uncontrollable hydration pace, MgO-based expansive concrete has mitigated all these limitations while enhancing strength and durability. It has been proven that compensating shrinkage with MgO expansion efficiently prevents thermal cracking of mass concrete, reduces the expense of temperature control systems, and speeds up the construction process. This paper briefly reviews the factors of MgO-based expansive agents that affect the characteristics of expansive concrete. The review indicates several parameters named as reactivity, thickness of water film, curing condition, additive ratio, and calcination condition that affects the expansibility, strength, soundness, durability, flowability, interior pores, crystal size, and hydration activity. Thus, comparative studies show the practicality of its usage while discussing future improvements.