ABSTRACT A purge and trap concentrator coupled to gas chromatography-pulsed flame photometric detector(GC-PFPD) after in situ ethylation with sodium tetraethylborate(NaBEt4) was used to analyze organotin compounds in water samples. The sample glassware with 5.5 ml water sample, 1.5 ml derivatizing reagent as well as 2 ml buffer solution was installed to purge and trap system, and then all steps were performed automatically, including ethylation, purge and trap, concentration, chromatography seperation and detection. Parameters including NaBEt4 concentration, purge flow rate, purge time, desorb time, the pH of buffer solution, H2 flow rate and the voltage of photomultiplier tube(PMT) of PFPD , which influence the speciation of organotin compounds were optimized. Method detection limits for dibutyltin and tributyltin were 0.50 and 0.46 ng as Sn/L, respectively. The calibration graphs were linear up to 2 orders of magnitude. Surface water samples collected from fourteen different locations of Kaohsiung harbor were analyzed. The concentration of dibutyltin ranged from nondetected(ND) to 272.2 ng as Sn/L and tributyltin ranged from nondetected to 105.4 ng as Sn/L. Recovery percentage for dibutyltin and tributyltin ranged from 88.9-95.3 %.