甲基橙是一种常用的酸碱指示剂或pH指示剂。

• 橙黄色粉末或鱼鳞状晶体有时显红色。
• 微溶于水，较易溶于热水，不溶于乙醇等有机溶剂。

• 又名做金莲橙D、（酸性）Ⅲ号橙
• 甲基橙（methyl orange）本身为碱性，变色范围为pH:3.1~4.4
• pH<3.1时变红，pH>4.4时变黄，pH在3.1~4.4时呈橙色。

Methyl orange is a pH indicator frequently used in titrations because of its clear and distinct colour change. Because it changes colour at the pH of a midstrength acid, it is usually used in titrations for acids. Unlike a universal indicator, methyl orange does not have a full spectrum of colour change, but has a sharper end point. Methyl orange shows orange colour in acidic medium and yellow colour in basic medium.