Three new diketopiperazine derivatives (DKPs), saroclazines A-C (1-3) along with three known DKPs (4-6) were isolated from mangrove-derived fungi Sarocladium kiliense HDN11-84. Saroclazines A-B (1 and 2) possessed a free amide structure, which was first found in sulfur-containing aromatic DKPs. Their structures were elucidated by NMR, HRESIMS and X-ray. The cytotoxic activity of new compounds (1-3) was tested against HeLa cell lines, among which compound 2 showed an IC