In this work, novel 2D type-II p-n heterojunctions La2Ti2O7/In2S3 have been fabricated. The heterojunctions exhibit much improved photocatalytic activity over individual moieties and their physical mixtures in which 18 fold increment in hydrogen production has been achieved under visible light illumination (W. a. 400 nm). Their superior activities stem from intimate face-to-face contact between La2Ti2O7 and In2S3 in the heterojunctions which guarantee facile charge interchange. Photoelectrochemical analysis suggests that efficient charge separations occur at the interfaces of the heterojunctions and contributes to a prolonged charge lifetime as well as the much enhanced photocatalytic activities. Such a simple strategy by fabricating ultrathin type-H p-n heterojunctions also warrant promising applications in other areas such as optoelectronics, sensors etc. whereby efficient charge separations are needed.