High frequency ultrasound (>15 MHz) is used in the fields of pre-clinical, intravascular, ophthalmology and superficial tissue imaging. Tissue-equivalent phantoms have previously been developed to enable relevant quality assurance measurements for frequencies lower than 15MHz but to date limited data is available on the acoustic properties of tissue equivalent material at frequencies higher than 15MHz. In this study, the acoustic attenuation of an International Electromechanical Commission (IEC) agar based tissue mimicking material (TMM) was measured over the frequency range of 12 - 47 MHz at 21 °C ± 1 °C using a broadband substitution technique. By applying a polynomial curve fitting function to the measured data the attenuation (dB·cm -1) was found to vary with frequency f(MHz) in the form of 0.39 f + 0.0069 f 2. This result is comparable to the published result at lower frequencies.