Core-shell electrocatalyst, in which a Pt atomic layer covers a nano-size core of a different metal, is attractive in reducing Pt usage for PEFC cathode electrocatalyst. Whilst such core-shell electrocatalysts exhibit very high mass activity for oxygen reduction reaction (ORR), their cost and durability still remain as a challenge. If inexpensive and thermochemically-stable conductive oxide could be applied to the core instead of a noble metal, cost reduction and durability improvement of such core-shell electrocatalysts may be expected. In this study, we try to develop oxide-core Pt-shell electrocatalysts by directly depositing Pt on SnO2 at an atomic level via a photochemical preparation procedure. SnO2 cores with a diameter down to ca. 3 nm could be prepared by comparing various preparation procedures of Sn02 and types of carbon-based materials acting as conductive fillers. Electrochemical activities of such oxide-core Pt-shell electrocatalysts are characterized and discussed.