Sol--gel transitions in gelatin are studied using a plano-concave resonator method for measuring ultrasonic velocity and absorption in the 0.2- to 3-MHz range, and also using a surface-wave method for measuring shear elasticity and viscosity in the hundreds of Hz range. The temperature dependences demonstrate the small decrease in ultrasonic velocity and the large increase in absorption upon gelation. These results show marked contrast with those of the low-frequency surface-wave measurements that agree with the percolation theory. The frequency dependence of ultrasonic absorption indicates a distribution of relaxation time. The mechanism of the ultrasonic behaviors is discussed in terms of the random coil--helix transition and hydration of gelatin molecules.