  In this paper, we show that for a simply connected CW complex $Y$ with
$H^{*}(Y;\mathbb{Q})$ of finite dimension, if $H^{*}(Y;\mathbb{Q})$ is
concentrated in degrees $\leq 3$, then the rationalization $Y_\mathbb{Q}$ is
formal. As an application, we show that the spatial realizations of simply
connected Sullivan algebras with rational homology concentrated in degrees
$\leq 3$ are formal.
