甲基红（methyl red），是一种常用的酸碱指示剂。

由邻氨基苯甲酸与亚硝酸作用发生重氮化生成重氮盐，然后与N,N-二甲基苯胺偶联制得：

Methyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder. Methyl red is a pH indicator; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a pK_a of 5.1. Murexide and methyl red are investigated as promising enhancers of sonochemical destruction of chlorinated hydrocarbon pollutants.Methyl red is classed by the IARC in group 3 - unclassified as to carcinogenic potential in humans.