  By $I$-method, the interaction Morawetz estimate, long time Strichartz
estimate and local smoothing effect of Schr\"odinger operator, we show global
well-posedness and scattering for the defocusing Hartree equation $$\left\{
\begin{array}{ll} iu_t + \Delta u &=F(u), \quad (t,x) \in \mathbb{R} \times
\mathbb{R}^4 u(0) \\ &=u_0(x)\in H^s(\mathbb{R}^4), \end{array} \right. $$
where $F(u)= (V* |u|^2) u$, and $V(x)=|x|^{-\gamma}$, $3< \gamma<4$, with
radial data in $H^{s}(\mathbb{R}^4)$ for $s>s_c:=\gamma/2-1$. It is a sharp
global result except of the critical case $s=s_c$, which is a very difficult
open problem.
