A series of poly(ethylene glycol)-block-poly(ε-caprolactone)-block-poly(ethylene glycol) (PEO-PCL-PEO) triblock copolymers were prepared and then used for the investigation of the effects of the ratio of ε-caprolactone to poly(ethylene glycol) (i.e., [CL]/[EO]) on the physical properties and release behavior of micro- and nano-capsules of vitamin derivatives. As model drugs, retinol and ascorbic acid-2-glucoside were used. For release behavior and proliferation of skin cell, artificial skin (Neoderm(R)) and hairless mouse were studied. In order to elucidate the role of PEO-PCL-PEO triblock copolymers during the drug permeation into skin layer, fluorecein isothiocyanate (FITC) was conjugated to the copolymers and monitored by using confocal laser scanning microscopy. The effects of [CL]/[EO] on the physical properties and release behavior of O/W (or W/O/W) emulsions will be discussed. [Figure Description] (a) Plot for the number of epidermis cell layers vs. PEO-PCL-PEO triblock copolymers. Optical microscope images of the cross-sectional view of the artificial skin cultivated with retinol emulsion for 2 weeks: (b) control (without retinol treatment), (c) with 1 wt.% of P-222, (d) with 1 wt.% of P-232, (e) with 1 wt.% of P-242, (f) with 1 wt.% of P-252, (g) with 3 wt.% of P-222, (h) with 3 wt.% of P-232, (i) with 3 wt.% of P-242, and (j) with 3 wt.% of P-252. n indicates the number of epidermis cell layers. Stratum corneum was separated from the epidermis layer while microtoming. (This work was supported by MOCIE, NGNT No. 10024160)