A phantom has been designed and fabricated to explore the potential benefits of tissue harmonic ultrasound imaging (THI) in prostate brachytherapy. Transverse and sagittal images of the phantom were acquired using 6, 9 and 12 MHz ultrasound frequencies in brightness (B) mode and 10 and 12 MHz in THI mode. The imaging parameters such as dead zone, depth of penetration, geometrical accuracy, axial and lateral resolution, contrast resolution and signal to noise ratio (SNR) in B‐mode were compared with those in THI‐mode. It was found that the dead zone is 1mm at all frequencies of both B‐mode and THI‐mode. The depth of penetration decreases insignificantly in THI mode, while contrast resolution and SNR improves. The axial resolution in THI mode (12 MHz) is ∼45% higher than B‐mode (6 MHz). The lateral resolution in THI mode (12 MHz) is ∼50% higher in the near zone and ∼10% higher in the far field than corresponding values in B‐mode (6 MHz). In general harmonic images are clearer, less noisy and display fewer artifacts than B‐mode images. This phantom study demonstrates that THI‐mode has the potential to provide better images of the prostate, which may help in prostate volume identification and improved treatment planning. An improvement in target localization has a potential to improve the treatment outcomes and reduction in the treatment related complications.