3. In an ellipse, $O$ is the center, $P$ is the endpoint of the minor axis, $F_{1} 、 F_{2}$ are the two foci, it is known that $\left|F_{1} F_{2}\right|=3$, the distance from point $O$ to the line $F_{1} P$ is 1. Then the eccentricity of the ellipse is $\qquad$
3. $\frac{\sqrt{5}}{3}$.

Let $2a$ and $2b$ be the lengths of the major axis and minor axis of the ellipse, respectively.
Thus, $|OP|=b$, and $\left|P F_{1}\right|=a$.
Let $O H \perp F_{1} P$ at point $H$. Then,
$\frac{b}{a}=\sin \angle P F_{1} O=\frac{|O H|}{\left|O F_{1}\right|}=\frac{2|O H|}{\left|F_{1} F_{2}\right|}=\frac{2}{3}$.
Therefore, the eccentricity of the ellipse is
$$
e=\sqrt{1-\left(\frac{b}{a}\right)^{2}}=\frac{\sqrt{5}}{3} .
$$