Yes, it is possible to fit uPVC windows in a stone wall. However, this is often a more complicated procedure than fitting a uPVC window into a brick wall.

Modern UPVC window frames form an integrated system that includes hinges, locking mechanisms and the supporting frame and glass.  The frames are fitted to the size of the opening in your wall and then mounted in place and screwed directly into the wall itself.  To ensure a perfect, gap-free and draught-free fit, filler is added around the window frame to compensate for any inconsistencies in the shape of the aperture.

Brick walls tend to have fewer inconsistencies in the shape - after all bricks are uniformly made and have completely straight edges, while stone blocks will usually have a slightly rounder edge to them.  This means that the window apertures may require additional preparation to fit your new windows.

Your installer will be able to advise you about the best process for fitting your new windows to ensure that they perfectly complement your home.