For $1\leq p\leq \infty$ and $\alpha>0$, Besov spaces $B^p_\alpha$ play a key role in the theory of $\alpha$-M\"obius invariant function spaces. In some sense, $B^1_\alpha$ is the minimal $\alpha$-M\"obius invariant function space, $B^2_\alpha$ is the unique $\alpha$-M\"obius invariant Hilbert space, and $B^\infty_\alpha$ is the maximal $\alpha$-M\"obius invariant function space. In this paper, under the $\alpha$-M\"obius invariant pairing and by the space $B^\infty_\alpha$, we identify the predual and dual spaces of $B^1_\alpha$. In particular, the corresponding identifications are isometric isomorphisms. The duality theorem via the $\alpha$-M\"obius invariant pairing for $B^p_\alpha$ with $p>1$ is also given.
