The current work investigates the influence of seawater on morphological properties during the hydration process of tricalcium silicate (C₃S) at 3, 7, 14, and 28 days to better understand the effect of salinity (highly soluble salts) of seawater on the microstructural evolution of hydration products. The mechanism of the chemical reaction of highly soluble salts, e.g., Na₂SO₄ and CaCl₂, with hydrated C₃S was also demonstrated. The presence of highly soluble salts in seawater accelerates the hydration of C₃S significantly due to releasing a significant amount of Ca²⁺ ions from the hydrated C₃S (as CH and CSH), which participated in the chemical reaction to produce a certain amount of gypsum crystals that was more than that in distilled water, which has been shown by SEM characterization. TEM analysis revealed the growth of sharp rod-like CaSO₄·2H₂O crystals together with some thin and tiny wrinkled CSH that formed. Seawater promotes the hydration of C₃S, pointed out by the expedited heat flow and raised heat of hydration. FTIR spectroscopy has been used to characterize and observe the dynamics of variation in the formation of calcium silicate hydrate (CSH), portlandite (CH), and gypsum (Gy) throughout the hydration process of C₃S with seawater in comparison with distilled water. XRD analysis revealed that the peak intensities of the portlandite and gypsum of the hydrated C₃S in seawater are higher than the comparable peaks in distilled water.