Data on handline fishery from a Thai-flagged fishing vessel were collected by an onboard observer during a fishing trip between April and May 2024 to identify fishing grounds and analyze total catch and length of species managed by the IOTC. The main fishing gear used by the vessel was otter board trawl, with handline as secondary gear. The study found that, among 42 days of handline fishing, IOTC-managed species was caught on 14 days, with all 14 days being observed. The fishing grounds were found in the high seas of the western Indian Ocean between latitude 09º 41ˊ and 10º 33ˊ south and longitude 61º 13ˊ and 61º 48ˊ east. The target species of the handline fishery were trevallies and snappers. Kawakawa (Euthynnus affinis) was the only one IOTC-managed species caught accidentally as bycatch. The total catch was 130.8 kg. The fork length ranged from 59 – 79 cm with an average of 66.31 cm. This study is the first to focus on a Thai fishing vessel using handline to catch IOTC-managed species.