The influence of cow manure ash (CMA) particle size distribution on some rheological properties of cement paste is the experimental basis for the application of CMA to concrete. Some research studies have been conducted with the purpose of studying this influence. The particle size distribution of CMA particles was measured by laser particle size analyser. The CMA particles in the cement paste samples constituted 5, 10, 15 and 20% of the total cement mass. The apparent viscosity of cement paste was measured with a rotational viscometer; the yield stress and plastic viscosity were calculated by fitting method. Correlations between CMA particle size distribution and some rheological properties (especially steady flow properties) were tested using a grey correlation analysis. The results of the correlation analysis show that: increasing the particle content of 3–32 μm and 32–65 μm size, especially the former, reduces the yield stress value, and increases the plastic viscosity of the slurry viscosity, except for at the level of 15% addition.