Several short-chain (dihexanoyl-, diheptanoyl-, and dioctanoyl-) phosphatidic acid (PA) molecules have been synthesized and characterized as water-soluble lipids for studies of cell activation and the interaction of negatively charged lipids with specific proteins. These species aggregate to form large polydisperse micelles. Critical micelle concentration (CMC) values of the dianions in 0.10 M NaCl are similar to those for the corresponding chain length phosphatidylcholine (PC) species. Surface properties suggest that the dianion has an area per molecule comparable to that of PC molecules, while the monoanion has a greatly reduced area, closer to twice the value of the two fatty acyl chains. This difference may be useful in understanding pH effects of protein-PA interactions.