Abstract <p>The effect of ultrasonic treatment modes on the microstructure and structural and rheological properties of oil emulsions with distilled water and formation water was studied. The emulsions were treated in an ultrasonic field (frequency, 22 kHz; intensity, 2, 6, and 18 W/cm²). The microstructure of the emulsions was analyzed using an AXIO LAB.A1 optical microscope (Carl Zeiss, Germany). The analysis of variances of the micrographs of the emulsions was performed to reveal the effect of the treatment conditions and the type of dispersed phase on the mean droplet diameter, dispersion, and position of the peak of water droplet size distribution in the emulsion. The rheological parameters of the emulsions before and after ultrasonic treatment were measured using a HAAKE Viscotester iQ rheometer (Thermo Scientific, the United States). For highly viscous oil with a high content of resin–asphaltene components, the degree of dispersion of water droplets decreased after pulsed ultrasonic treatment at a field intensity 6 W/cm² in two modes (5 cycles with 10 s of operation and 10 s of rest; 10 cycles with 5 s of operation and 5 s of rest).</p>