For \(\alpha >-1\) we established the optimal estimate of the type \(|Df(z)|\le \phi (|r|)\Vert f^{*}\Vert _{p}\) where f is \(\alpha -\)harmonic mapping defined in the unit disc belonging to the Hardy space \(h^{p},\)\(p\ge 1,\)\(\alpha +\frac{2}{p}\ge 0\) and \(f^{*}\) is its boundary function.