During a severe accident scenario of nuclear power plants, a steam explosion may occur when a substantial amount of molten core materials is rapidly ejected into a volatile coolant (water) pool, forming so-called Fuel-Coolant Interactions (FCI). The steam explosion poses a serious threat to the containment integrity. It is therefore important to understand and suppress the risk of steam explosions. The present study is concerned with mechanism of steam explosion on effect of coolant composition, i.e., to investigate how seawater impacts steam explosion energetics. For this purpose, a set of preliminary experiments were performed on spontaneous steam explosion by delivering a single molten tin droplet into a cold water pool at different levels of salinity on MISTEE facility. This paper presents the comparative results of the experimental data, including the influences of the salinity on probability of spontaneous explosion occurrence, explosion depth underwater and available thermal energy of droplet for explosion, as well as fragmentation (particle size distribution of debris % by mass). As the reference of the comparisons, the steam explosion characteristics from experiments in deionized water were employed. We experimentally observed that probability of spontaneous explosion occurrence increased in seawater, and more thermal energy of droplet was available for explosion when a droplet was self-triggered. The seawater at high salinity (35.16 g/kg) appeared remarkable enhancement on fragmentation. More experimental data are still needed to reveal more details and to develop a model for better understanding and prediction for the effects. The present data was helpful for prudential assessment on the seawater effects when it was employed as ultimate emergency cooling if NPPs located on sea coasts encounter Fukushima-like accidents.