We investigated the distribution and the in-situ target strength (TS, dB) of the skipjack tuna Katsuwonus pelamis associated with light falling-nets in the South China Sea using the Simrad EY60 scientific echosounder. The volume backscattering strength (Sv, dB), TS, and mean number of fish per sampled volume (N_V) were studied. The average fork length of skipjack tuna in the S13, S14, and A12 stations were (362.20±35.73) mm, (357.66± 36.61) mm, and (366.70±36.43) mm, respectively. There was no significant difference in the average fork length among the three stations (P>0.05). Within the depth range of 10–50 m, the mean S_V change pattern of the three stations at different time phases was similar. Before the fishing lights were turned on (18:00–19:00), the K. pelamis was mainly distributed at a water depth of 40–50 m; after the lights turned on, the K. pelamis was gradually attracted and floated, and thus the depth corresponding to the peak of the S_V distribution curve became shallower. With the increase of lighting time (20:00–21:00), the K. pelamis was stably distributed at a depth range of 10–30 m. In the depth range of 10–50 m, the number of individual signals at the three stations in different time phases was also similar to the mean depth change pattern. Before the fishing lights were turned on (18:00–19:00), the signals were mainly distributed at a depth of 35 m, and few signals were detected. After the lights were turned on, K. pelamis were gradually attracted and floated, resulting in a shallower mean depth of the signals, and the number of signals increased significantly. There were no N_V limit values at the three stations in this study, and all cells can be used for the in-situ TS calculation. The mean in-situ TS was (–51.84±3.84) dB at the S13 station, (–49.87±3.72) dB at the S14 station, and (–49.68±2.96) dB at the A12 station. The in-situ TS of K. pelamis at the three stations were non-normally distributed (P<0.05). These results help us better understand the fish behavior and acoustic characteristics under the conditions of light trapping and also set up a technical foundation for future acoustic evaluation.