Abstract. In this paper, we show that every compactification, which is a quasi-F space, of a space X is a Wallman compactification and that for any compactification K of the space X, the minimal quasi-F cover QF K of K is also a Wallman compactification of the inverse image Φ −1 K (X) of the space X under the covering map Φ K : QF K −→ K. Using these, we show that for any space X, βQF X = QF βυX and that a realcompact space X is a projective object in the category Rcomp # of all realcompact spaces and their z # -irreducible maps if and only if X is a quasi-F space.