The effects of graphene oxide (GO) on the yield stress-pH of -Al2O3 (alumina) suspensions were investigated. For micron-sized platelet alumina suspensions, micron-sized GO additive increased the maximum yield stress by as much as six-folds. This was attributed to GO-mediated bridging interactions between the platelet particles. This type of bridging interactions was much less effective with submicron-sized, spherical, and irregular shape alumina. Adsorption of the anionic GO reflected by the shift of pH of zero zeta potential to a lower pH is particularly high for platelet alumina. The 1.0 dwb % GO concentration added is sufficient to reinforce each platelet particle-particle bond, assisted by a directed GO-platelet interaction configuration. This is, however, not true with submicron-sized particles as the particle concentration increases sharply with the inverse of the particle diameter to power of 3. Moreover, a GO sheet can adsorb several submicron-sized particles and this does not produce the right interaction configuration. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 3633-3641, 2013