Diffractive Contribution to $g_1$ Structure Function at Small $x$

We study the small $x$ diffractive contribution to the spin--dependent proton structure function $g_1(x)$. We find that the $x\to 0$ behaviour of $g_1(x)$ has a singular form like $1/(x^\alpha \ln^2(x))$ with $\alpha \sim 0.2-0.3$.