This paper describes a new optical chemical sensor based on 1,4-bis(1,3-benzoxazoly-2)benzene(BBOB) as a sensing material. The sensing membrane incorporating BBOB is able to selectively extract ethacrynic acid (EA) from the sample solution into the organic membrane phase, and reversibly forms a 1:1 complex. This process resulted in a change in fluorescence signal. The optimized sensing membrane could be used for the determination of EA from 8.0 × 10−2mol·L−1to 1.0 × 10−4mol·L−1. Besides the high reproducibility of the optical signals, very short response times of less than 30s were achieved. The optrode membrane was successfully applied to the determination of EA in commercial tablets. The results showed a good agreement with those obtained by the pharmacopoeia method.