Biological N₂ fixation in marine environments is a major component in the ocean nitrogen budget and plays an important role in global carbon cycles through the sequestration of atmospheric carbon dioxide and production of marine organic matter. N₂ fixation could be regulated by the abundance and chemical speciation of nutrients and many trace elements in seawater. Recent studies have revealed that N₂ fixation is much more widespread in marine environments than previously thought. However, little is known about the N₂ fixation in the Taiwan Strait, especially on N₂ fixation rates, and their relationship with environmental parameters. The major objectives of this study were to determine the N₂ fixation rates and their spatial distributions and to explore major physicochemical controlling factors in the south Taiwan Strait. During June and July 2011, seawater samples were collected from ten stations at two transects in the south Taiwan Strait for the measurements of N₂ fixation rate using the ¹⁵N₂ tracer assay. Particulate nitrogen and its isotopic composition were measured with an elemental analyzer (Carlo Erba NC 2500) coupled with a Finnigan MAT Delta^plus XP isotope ratio mass spectrometer. Reproducibility of nitrogen isotope measurements (in terms of δ¹⁵N) was within 0.2‰. Our results showed that N₂ fixation rates in the south Taiwan Strait ranged from 168-1080 nmol m^-3 d^-1 with an average of 537 nmol m^-3 d^-1. Most of the high rates were observed at subsurface layers. The depth-integrated N₂ fixation rates were 11-40 μmol m^-2 d^-1 with an average of (23±10) μmol m^-2 d^-1. The distribution of the N₂ fixation rates showed regional variations with influence from water masses with distinctive temperature and salinity. Higher N₂ fixation rates were mostly observed in the regions influenced by the Kuroshio, with an average of 31 μmol m^-2 d^-1, while lower rates occurred in the upwelling and river plume regions with an average of 15 μmol m^-2 d^-1. This spatial distribution pattern indicated that biological N₂ fixation was largely impeded by the low temperature and the high concentration of dissolved inorganic nitrogen in the south Taiwan Strait. The contribution of N₂ fixation in the study area could be further quantified based on the δ¹⁵N signatures of suspended particles which could be significantly depleted during N₂ fixation. Indeed, a negative correlation between the δ¹⁵N signatures of suspended particles and N₂ fixation rates was observed regardless of using all data points or depth-averaged values within the water column. This indicated that ¹⁵N-depleted particles were largely derived from the enhanced N₂ fixation, supporting the use of nitrogen isotopic composition (δ¹⁵N) of suspended particles as a potential indicator of N₂ fixation in the south Taiwan Strait. Further studies are needed to better elucidate the relationship between N₂ fixation rates and limiting elements and their chemical speciation, and thus the physical and biogeochemical controls on N₂ fixation in the south Taiwan Strait.