“Fact” in Chinese is 事实 (shìshí).
这是事实。
It's the truth.
Example sentence from Tatoeba (CC BY 2.0).
Not to be confused with: 逝世 (shìshì, to pass away) · 适时 (shìshí, timely) · 时事 (shíshì, current trends; the present situation; how things are going) · 时时 (shíshí, often) · 实施 (shíshī, to implement)