Oxide heterojunctions made of p-type La0.8Sr0.2MnO3 (LSMO) and niobium-doped n-type SrTiO3 (STO:Nb) have been fabricated by the pulsed laser deposition (PLD) technique and characterized under UV light irradiation by measuring the current-voltage, photovoltaic properties and the junction capacitance. It is shown that the heterojunctions work as an efficient UV photodiode, in which photogenerated holes in the STO:Nb substrate are injected to the LSMO film. The maximum surface hole density Q/e and external quantum efficiency gamma are estimated to be 8.3 X 10(12) cm(-2) and 11% at room temperature, respectively. They are improved significantly in a p-i-n junction of LSMO/STO/STO:Nb, where Q/e and gamma are 3.0 X 10(13) cm(-2) and 27%, respectively. (C) 2004 Elsevier Ltd. All rights reserved.