三甲苯是苯环上连接三个甲基而形成的烃类化合物，分子式为 C₆H₃(CH₃)₃ ，包括三个同分异构体：

• 均三甲苯，即1,3,5-三甲基苯，最熟知的异构体
• 偏三甲苯，即1,2,4-三甲基苯
• 连三甲苯，即1,2,3-三甲基苯

The trimethylbenzenes constitute a group of substances of aromatic hydrocarbons, which structure consists of a benzene ring with three methyl groups (–CH₃) as a substituent. Through their different arrangement, they form three structural isomers with the molecular formula C₉H₁₂. They also belong to the group of C₃-benzenes. The best-known isomer is mesitylene.