A manufacturing method is developed for the fabrication of sub-50 nm current-perpendicular-to-plane (CPP) spin valve sensors. A feature size reduction process is used to reduce the feature size from above 100 nm, which is determined by lithography process, to sub-50 nm. The approach is to use the isotropic wet etch of a hard mask to reduce its transverse dimension and transfer the reduced dimension to CPP sensors by a subsequent etch process. In this approach, the sensor size is controlled by the wet etch, which can, in principle, be reduced to several nanometers. For CPP sensor fabrication, resist flattening and etch back processes are developed to avoid the alignment issues for the opening of sensor contacts. Using this approach, CPP sensors with sub-50 nm track width have been fabricated. Magnetoresistance measurement shows that the sensor has a reasonable performance.