Radial modulation imaging is a new medical imaging technique based on dual‐frequency insonation of ultrasound contrast agents. The difference in echo between a high frequency 'imaging' pulse transmitted at either the compression or rarefaction phase of a low frequency 'modulating' pulse is detected by regular correlation techniques. Little is however known about the contrast agent microbubble dynamics in a dual‐frequency ultrasound field, which were investigated in this study. Using a high‐speed camera system, the radial excursions of single phospholipid‐coated microbubbles were recorded. The microbubbles were simultaneously insonified with 2.5 cycles pulse at 0.5 MHz and 30 kPa and a 32 cycles pulse at 3.75 MHz and 80 kPa. The microbubbles studied had diameters ranging from 1.1 ‐ 5.2 μm. Microbubbles smaller than 1.4 μm frequently showed shrinkage. Microbubbles larger than 2.6 μm showed low (< 8 dB) or no amplitude modulation of the high frequency radial excursion. Microbubbles with diameters between 1.4 and 2.6 μm showed high amplitude modulation (up to 25 dB) and strong compression‐only oscillation, which both may be explained by nonlinear shell properties. The observed behaviour is beneficial for the detection of contrast agents.