Concrete is a material that the mechanical properties of which change over time. This change is due to chemical reactions within the concrete known as hydration. One of these properties is the modulus of elasticity and longitudinal wave velocity, which has a direct relation with the concrete age and its setting. Just after the materials mixing, the concrete setting is fast, and over time its rate decreases. Here, a series of cubic concrete specimens are prepared and changing in longitudinal wave velocity and modulus of elasticity in different ages is monitored during the process of curing and a relationship has been presented. Materials specifications impact and concrete mixing ratios, including the water to cement ratio and fine to coarse aggregates ratio is studied. Ultrasonic wave velocity has been increased faster at early ages of specimens where the concrete setting process is fast and in last days, rates of increasing the longitudinal wave velocity decreases. An increase in the water to cement ratio leads to increases in the longitudinal wave velocity over time. The empirical equations have been formulated as logarithmic curves. These empirical equations have been developed and a model with more efficiency and precision has been presented. These empirical equations can be used in the analytical and numerical analysis of structures. These models can be used to determine the loading time of concrete structures and to predicting their other physical and mechanical properties, such as strength and stiffness.