Is there any injections to decrease size of nose ?

Injectables augment or add to the volume of the facial structures.  So, no, there are currently no injectables that decrease the size of the nose.  Having said that, there are instances when augmenting the nose can actually make it appear smaller.  For instance if you have a very wide, flat nasal dorsum, then augmenting the central dorsum will give the appearance of a smaller nose on frontal view.  Additionally, some people with a "bump" on profile view in the mid portion of their nose actually have a low nasal starting point and radix augmentation with filler (or surgery) can make their nose look smaller.  Photos would help, but honestly, the best solution is for you to see a well respected rhinoplasty surgeon to evaluate your entire face and discuss the options with you.

It seems hard to believe but my colleagues and I as well Dr. Kent Remington in Canada perform a filler injection on the nose that will give the effect of less prominence or projection for certain noses.  We place a hyaluronic acid filler (Perlane or Juvederm) in the top or bridge of a nose that is particularly concave, and it serves to diminish the projection of the tip.  

Injections can be used to improve nasal contours but you cannot add liquid material to decrease the size of any structure. Consult with a rhinoplasty specialist to discuss your options.