Encapsulation effciency is affected by several parameters such as oil-droplet diameter, solid and oil contents, as well as by the processing conditions of spray drying. The surface-oil ratio is the most important parameter that estimates the shelf life of fish oil in spray-dried powders. In the present study, sodium caseinate (3 wt%), maltodextrin (DE = 8, 11, 19, 25, and 40) as the wall material, and fish oil as the core material were used to form spray-dried powders with 30, 40, 50 and 60 wt% of oil load of the total solid content. The oil load is expressed as a weight percentage of additional oil to the total solid content. Feed emulsions were prepared using a rotor-stator homogenizer at 8000 rpm and/or a high-pressure homogenizer at 20 or 100 MPa. The effects of oil-droplet diameter and particle diameter on the surface-oil ratio and the encapsulation effciency of emulsified spray-dried fish oil were investigated. The surface-oil ratio was remarkably increased when the ratio E = (d(e)/d(p)) of the average reconstituted oil-droplet diameter (de) to the average particle diameter (d(p)) was higher than 0.01. The surface-oil ratio was defined as the weight ratio of surface oil to total oil in the powder. The encapsulation effciency y was related to E by the equation y = (1-2E)(3). The oil-droplet diameter might affect the stability of fish oil in spray-dried powders.