Let $B\,=\,{{B}_{n}}$ be the open unit ball of ${{C}^{n}}$ with volume measure $v$, $U\,=\,{{B}_{1}}$ and $B$ be the Bloch space on $U.\,{{\mathcal{A}}^{2,\alpha }}(B)$, $1\,\le \,\alpha \,<\infty $, is defined as the set of holomorphic $f\,:\,B\,\to \,C$ for which

$$\int_{B\,}{{{\left| f(z) \right|}^{2}}}{{\left( \frac{1}{\left| z \right|}\,\log \frac{1}{1\,-\left| z \right|} \right)}^{-\alpha }}\,\frac{dv(z)}{1\,-\,\left| z \right|}\,<\,\infty $$

if $0\,<\,\alpha \,<\infty $ and ${{\mathcal{A}}^{2,1}}(B)\,=\,{{H}^{2}}(B)$, the Hardy space. Our objective of this note is to characterize, in terms of the Bergman distance, those holomorphic $f\,:\,B\,\to \,U$ for which the composition operator ${{C}_{f}}\,:\,B\,\to \,{{\mathcal{A}}^{2,\alpha }}(B)$ defined by ${{C}_{f}}(g)=g\,\text{o}\,f\text{,}\,g\in B$, is bounded. Our result has a corollary that characterize the set of analytic functions of bounded mean oscillation with respect to the Bergman metric.