  We prove a rearrangement inequality for the uncentered Hardy-Littlewood
maximal function $M_{\mu}$ associate to general measure $\mu$ on $\mathbb{R}$.
This inequality is analogous to the Stein's result
  $cf^{**}(t)\leq(Mf)^{*}(t)\leq C f^{**}(t)$, where $f^*$ is the symmetric
decreasing rearrangement function of $f$ and $f^{**}(t)=\int_0^tf^*(x)dx$.
  Moreover, we compute the best constant of $M_{\mu}$ on
  $L^{p,\infty}(\mathbb{R},d\mu)$.
