With the continuous increase of infrastructural construction worldwide, the supply of river sand and fresh water for making concrete encountered enormous shortage, especially for coastal regions. To alleviate this problem, researchers have started to investigate the possibility of consuming seawater and sea sand as alternatives. This paper reports the results of a comprehensive study on the mechanical and microstructural properties of seawater and sea sand concrete. Three types of concrete: seawater and sea sand concrete (SSC), sea sand concrete (SC), and ordinary concrete (OC), were prepared following two different water/binder ratio. Compressive strength, flexural strength, dynamic modulus of elasticity, and stress-strain relationship as well as microstructural analysis of all the concrete types were investigated. It was observed that the use of seawater and sea sand has led to an increase of the early age compressive strength but slightly decrease of the 28 days strength. The flexural strength of seawater and sea sand concrete, sea sand concrete has been ameliorated at 28 days, when compared, to ordinary concrete. The dynamic modulus of elasticity of concrete made with either seawater and sea sand or sea sand has been significantly enhanced, especially at the early age. X-ray diffraction pattern (XRD) and scanning electron microscopy (SEM) analyses further confirmed that sea sand and seawater have a remarkable effect on the surface morphology and the significant contrast from ordinary concrete due to the dominance of the ettringite phase with crystals that have a fibrous shape, which leads to a compacted and less porous structure and enhancement of the mechanical behavior.