丙二酸，也称缩苹果酸，是一个二羧酸，酸酐为二氧化三碳，化学式为CH₂(COOH)₂，可看作由丙烷的1,3-位两个氢原子被羧基取代形成。丙二酸及丙二酸酯是有机合成中的重要试剂。

• 丙二酸的钙盐为白色晶体，大量存在于甜菜根中。
• 丙二酸可作竞争抑制剂，在呼吸电子传递链中抑制琥珀酸脱氢酶（复合物II）。

Malonic acid (IUPAC systematic name: propanedioic acid) is a dicarboxylic acid with structure CH₂(COOH)₂. The ionized form of malonic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is malonic acid's diethyl ester. The name originates from the Greek word μᾶλον (malon) meaning 'apple'.