We report on a search for the doubly Cabibbo suppressed decay B+→D*+π0, based on a data sample of 657×106 BB̄ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find no significant signal and set an upper limit of B(B+→D*+π0)<3.6×10-6 at the 90% confidence level. This limit can be used to constrain the ratio between suppressed and favored B→D*π decay amplitudes, r<0.051, at the 90% confidence level. © 2008 The American Physical Society.