The present study was undertaken to develop a solid self-emulsifying drug delivery system of coenzyme Q 10 (CoQ 10 /s-SEDDS) with high photostability and oral bioavailability. The CoQ 10 /s-SEDDS was prepared by spray-drying an emulsion preconcentrate containing CoQ 10 , medium-chain triglyceride, sucrose ester of fatty acid, and hydroxypropyl cellulose, and its physicochemical, photochemical, and pharmacokinetic properties were evaluated. The CoQ 10 /s-SEDDS powder with a diameter of ca. 15μm was obtained by spray-drying, in which the CoQ 10 was mostly amorphized. The CoQ 10 /s-SEDDS exhibited immediate self-emulsification when introduced to aqueous media under gentle agitation, forming uniform fine droplets with a mean diameter of ca. 280nm. There was marked generation of reactive oxygen species, in particular superoxide, from CoQ 10 exposed to simulated sunlight (250W/m 2 ), suggesting potent photoreactivity. Nano-emulsified solution of CoQ 10 under light exposure underwent photodegradation with 22-fold higher degradation kinetics than crystalline CoQ 10 , although the CoQ 10 /s-SEDDS was less photoreactive. After the oral administration of CoQ 10 /s-SEDDS (100mg-CoQ 10 /kg) in rats, enhanced exposure of CoQ 10 was observed with increases in both C max and AUC of ca. 5-fold in comparison with those of orally administered crystalline CoQ 10 . From the improved physicochemical and pharmacokinetic data, the s-SEDDS approach upon spray-drying might be a suitable dosage option for enhancing nutraceutical and pharmaceutical values of CoQ 10 .