ClO3

ClO3 may refer to:

• The chlorate anion, $\mathrm{C}\mathrm{l}\mathrm{O}{\phantom{A}}_3{\phantom{A}}^{-}$
• Monochlorine trioxide, a hypothetical radical akin to chlorine dioxide
• The empirical formula for dichlorine hexoxide / chloryl perchlorate
• The perchloryl cation, $\mathrm{C}\mathrm{l}\mathrm{O}{\phantom{A}}_3{\phantom{A}}^{+}$