  It is shown that all solutions are bounded for Duffing equation $\ddot{x}+
x^{2n+1}+\sum_{j=0}^{2n}P_{j}(t)x^{j}=0,$ provided that for each $n+1\le j\le
2n$, $P_j(t)\in C^{\gamma}(\mathbb T)$ with $\gamma>1-\frac1n$ and for each
$0\le j\le n$, $P_j\in L(\mathbb T^1)$.
