Emulsified acids have been extensively used in the oil industry since 1933. Most of the available research and publications discussed mainly the application of emulsified acid in the field. A fair number of the published work also discussed in depth some of the emulsified acid properties such viscosity, stability and reactivity. However, all of the available research discussed the emulsified acid without sufficient details of its preparation. Beside their chemical composition, the ways emulsified acids are prepared cause significant differences in their physical properties. The characterization of emulsified acid by its droplet size and size distribution complements its chemical composition and gives the emulsified acid a unique description and thus reproducible properties. No previous study considered the impact of the droplet size on the characteristics and properties of emulsified acid. Therefore, the main objective of this research is to study the effects of the droplet size on various properties of emulsified acid such as viscosity, stability and reactivity. Results showed that the droplet size and size distribution have a strong effect on the stability, viscosity and diffusion rate of the emulsified acid. The results of this work are important because knowledge of the effect of the droplet size on major design parameters will guide the way emulsified acid is prepared and applied in the field.