The attenuation of longitudinal ultrasonic waves has been measured in single crystals of pure tin and tin doped with 0.0016, 0.0031, 0.0051 and 0.0093 at.% indium in the intermediate state in the frequency range 10-30 MHz. It is shown that the total attenuation in the intermediate state can be divided into two parts. The superconducting layers give rise to the oscillatory temperature dependent attenuation, while the normal layers and the boundary effect between the normal and superconducting layers produce a temperature independent constant attenuation. An exact estimate of the attenuation due to the superconducting layers has been made by combining the results of magnetic field dependence of the attenuation in the intermediate state at a fixed temperature much below T_c and the temperature dependent behaviour of attenuation in the intermediate state for the magnetic field value of ²/₃ H_c.