Recently Kiryakova and several other ones have investigated so-called multiindex Mittag-- Leffer functions associated with fractional calculus. Here, in this paper, we aim at establishing a new fractional integration formula (of pathway type) involving the generalized multiindex Mittag--Leffer function $E_{\gamma,k}[(\alpha_j,\beta_j)_m;z]$. Some interesting special cases of our main result are also considered and shown to be connected with certain known ones.