The characterization and optimization of the microstructures of materials pertaining to material properties is a primitive necessity to ensure the performance and service life of the materials and components. In the demand of new characterization and evaluation techniques, nondestructive ultrasonic techniques have shown a good potential to characterize the microstructures and mechanical properties of a wide variety of materials. Measurements of ultrasonic parameters such as velocity and attenuation can provide information on the structural and microstructural variations of those materials that have undergone the heat-treatment procedure. In the current review, the correlation of ultrasonic parameters with microstructural features of ferrous and nonferrous metals such as steels, aluminum, and superalloys is investigated. It is proven that ultrasonic parameters are closely correlated to the microstructural evolutions which frequently occur during the heat-treatment procedures in practical situations. To conclude, the ultrasonic measurements contribute to a feasible and accurate characterization of the materials and evaluation of their microstructures and mechanical properties in a straightforward, reliable, and fast, nondestructive manner for practical applications.