The surface composition of spray-dried sodium caseinate/lactose emulsions with different oil-phases were estimated by ESCA and the particle structure was studied by SEM before and after storage under humid conditions. After spray-drying, powders in which the oil phases consisted of fats with intermediate melting points like hardened coconut oil and butter fat had the highest surface coverage of fat, approx. 34 %. Powder with soy-bean oil as the oil phase had a surface coverage of fat of approx. 15 %. The high melting hardened rape-seed oil was almost completely encapsulated after spray-drying. After storage in a humid atmosphere, fat was released onto all the powder surfaces (surface fat after storage, between 50-65 %) except for those with hardened rape-seed oil in which the fat remained encapsulated. These observations are consistent with the powder structure observed by SEM. The surface composition estimated by ESCA for spray-dried sodium caseinate/lactose-containing emulsions with different amounts of soy-bean oil and a constant lactose/sodium caseinate ratio show an almost completely encapsulated oil-phase after drying. Storage of these powders in a humid atmosphere leads to a release of fat onto the powder surface even if the soy-bean oil content is low ( 1 % of the dry weight). Powders made from soy-bean oil emulsions with sodium caseinate alone exhibit a much lower degree of encapsulation than in the system where lactose is present.