The -5 mu m size fractions of two low rank British coals were used in zeta potential measurements. The electrophoretic behaviour was described by the Helmholta-Smoluchowski equation. The non-ionic reagents used for the adsorption tests were of diacetone alcohol and 2-ethylhexanol. Zeta potentials of both coals at various pHs were significantly different in the absence of the non-ionic reagents. Negligible variations were observed on the zeta potential curves of both coal particles in the presence of the non-ionic reagents used. It was concluded that the pH of coal particles in slurry is a principle parameter controlling the value of zeta potentials. As the zeta potential for Bickershaw coal particles was zero at about pH 5, the point of zero zeta potential was not observed for Rawdon coal particles. This is attributed to the functionality and the extent of oxidation of the coal surface.