We determine the integral extension groups $Ext^{1} (\Delta (h), \Delta (h(k)))$ and \\ $Ext^{k} (\Delta (h), \Delta (h(k)))$, where $\Delta (h), \Delta (h(k))$ are the Weyl modules of the general linear group $GL_n$ corresponding to hook partitions $h = (a,1^{b}), h(k) = (a+k,1^{b-k})$.