Adsorption of surfactant molecules, cationic as well as anionic, has been carried out on nanocrystals of magnesium oxide, prepared by an aerogel route (AP-MgO). Aerosil OT (AOT) and didodecyl dimethylammonium bromide (DDAB) have been chosen as examples of anionic surfactant and cationic surfactant, respectively. The adsorption studies were mainly carried out in nonaqueous media. For comparison, adsorption experiments were also carried out for two other magnesium oxide samples, namely, conventionally prepared MgO (CP-MgO) and commercial MgO (CM-MgO), which consist of microcrystals. The adsorption properties of the surfactants have been studied by determining the adsorption isotherms. The results have been interpreted on the basis of the fact that nanocrystals possess increased surface reactivity compared to microcrystals and particle shapes do have a role to play.