Two new phenylpropanoids, tagalphenylpropanoidins A-B (1-2), together with a known analogue, 2,3,6-trimethoxy-5-(1-propenyl)phenol (3), were isolated from the ethanolic extract of the Chinese mangrove Ceriops tagal. The structures of these compounds were determined by extensive spectroscopic analysis, including 1D and 2D NMR and HR-ESI-MS, as well as the comparison with data in the literature. Compound 3 was discovered from this plant for the first time. Cytotoxicities of the three compounds against MCF-7 and HL-60 cancer cell lines were also evaluated.