Five new cyclic peptides (including four heptapeptides and one octapeptide), reniochalistatins A–E (1–5), were isolated and characterized from the marine sponge Reniochalina stalagmitis collected off Yongxing Island in the South China Sea. Their structures were assigned on the basis of HRESIMS, 1D and 2D NMR spectroscopic data, and MALDI-TOF/TOF data for sequence analysis. The absolute configurations of all of the amino acid residues were determined using chiral-phase HPLC and Marfey’s analysis. The cyclic octapeptide reniochalistatin E showed biological activity in various cytotoxicity assays employing different tumor cell lines (RPMI-8226, MGC-803, HL-60, HepG2, and HeLa).