The numerical modeling of an electroosmosis flow in a rectangular three-dimensional rotating microchannel has been studied. The study’s goal is to calculate the flow’s development length, and as a novelty, a correlation is proposed to estimate the development length. The flow was simulated for angular velocity (ω) ranges of 0–9 and electric potential (φ) ranges of 0.1–0.3. The results were imported into the curve fitting toolbox to determine a correlation for the development length. The correlation was obtained as a function of angular velocity, electric potential, and hydraulic diameter. The results show that increasing both ω and φ leads to an increase in flow development length, where for constant φ, increasing ω from 0 to 9 results in a 20%–30% increase in development length. Furthermore, increasing φ from 0.1 to 0.3 for a constant ω raises development length by 35%–50%. The velocity field and its parameters, such as ω and φ, were analyzed and discussed.