壬酸，结构式CH₃(CH₂)₇COOH。

纯品为无色微有特殊气味的油状液体，工业品常呈淡黄色。有腐蚀性。不溶于水，溶于乙醇、乙醚和氯仿。

Nonanoic acid, also called pelargonic acid, is an organic compound composed of a nine-carbon chain terminating in a carboxylic acid with structural formula CH₃(CH₂)₇COOH. Nonanoic acid forms esters—nonanoates. It is a clear, oily liquid with an unpleasant, rancid odor. It is nearly insoluble in water, but very soluble in chloroform, ether, and hexane. It is commonly used in conjunction with glyphosate, a non-selective herbicide, for a quick burn-down effect in the control of weeds in turfgrass.