For a fibration (E,B,p) with fiber F and a fiber map f, we show that if the inclusion $i : F o E$ has a left homotopy inverse, then $G^f_n(E,F)$ is isomorphic to $G^f_n(F,E) oplus pi_n(B)$. In particular, by taking f as the identity map on E we have $G_n(E,F)$ is isomorphic to $G_n(F) oplus pi_n(B)$.