A new application of monoacidic dye is reported for the determination of pipethanate hydrochloride(PTH). The method is based on solvent extraction into chloroform of an ion-pair compound formed between methyl orange(MO) and PTH. PTH is determined by measuring absorbance of the extracts over the range of 2.0∼12.0㎍/㎖ at 420㎚. Best accuracy can be obtained for solutions containing 3.0∼8.0㎍/㎖. The color was stable for at least 5 days. The molar absorptivity was 2.88 × 10⁴ l, ㏖^(-1), ㎝^(-1). Molar ratio and continuous variation plots have a maximum at 0.5 ㏖ fraction of MO, indicating a 1 : 1 MO-PTH ratio