均三甲苯（又名1,3,5-三甲苯，C₉H₁₂）是苯环上三个氢对称地被三个甲基取代而得到的芳香烃。

用硫酸处理丙酮后蒸馏（发生羟醛缩合反应），或者将丙炔在硫酸作用下三聚，都可以制得均三甲苯。在这两个反应中，硫酸既作为催化剂，又作为脱水剂。

Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents symmetrically placed on the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenzene (hemimellitene). All three compounds have the formula C₆H₃(CH₃)₃, which is commonly abbreviated C₆H₃Me₃. Mesitylene is a colourless liquid with sweet aromatic odor. It is a component of coal tar, which is its traditional source. It is a precursor to diverse fine chemicals. The mesityl group (Mes) is a substituent with the formula C₆H₂Me₃ and is found in various other compounds.