Two new acridinium esters with a 2‐(succinimidyloxycarbonyl)ethyl side arm, namely 9‐(2,6‐dibromophenoxycarbonyl)‐10‐methyl‐2‐(2‐(succinimidyloxycarbonyl)ethyl)acridinium trifluoromethanesulfonate and 9‐(4‐(2‐(succinimidyloxycarbonyl)ethyl)phenoxycarbonyl)‐2,7‐dimethoxy‐10‐methylacridinium triflate, have been produced and characterized. The chemiluminescent properties and hydrolytic stabilities of the new acridinium esters have been investigated.