Abstract: To investigate the effects of low-salt stress on the growth of watercress (Oenanthe javanica) and the effectiveness of short-term domestication in enhancing its salinity tolerance, this study evaluated and compared the impact of low salt stress with salinity levels of 2, 4, 6, and 8 practical salinity units (PSU) and short-term domestication on salinity tolerance, growth, and physiological and biochemical characteristics of domesticated and undomesticated watercress over a 54 d period. The watercress was domesticated under hydroponic conditions by incrementally increasing the salinity by 2 PSU every 3 d. The results exhibited that after 54 d of salt stress, both the short-term domesticated and non-domesticated watercress survived up to 6 PSU salinity. Salinity and short-term domestication significantly affected watercress growth and biochemical processes of watercress. Compared to the control group, salt stress exceeding 2 PSU decreased the growth rates of fresh weight, plant height, root length, leaf number, and chlorophyll content in water dropwort by 126.0%–199.4%, 67.5%–124.0%, 63.4%–83.2%, 154.1%–325.0%, and 21.0%–52.6%, respectively. However, after acclimation, these declines were reduced to 40.7%–185.7%, 25.0%–83.5%, 37.8%–57.2%, 62.7%–294.7%, and 7.5%–37.8%, respectively. The relative water content in water dropwort leaves significantly decreased by 4.8%–6.4% under salt stress, but only increased by 2.9%–3.4% after acclimation. Salt stress significantly increased the malondialdehyde (MDA) and proline contents in water dropwort leaves by 39.6%–52.9% and 25.1%–30.9%, respectively, whereas after acclimation, these increases were 25.4%–46.8% and 36.1%–43.3%, respectively. Reactive oxygen species (ROS) content in water dropwort leaves significantly increased by 23.4%–29.5% under salt stress, but only by 7.4%–22.1% after acclimation. The activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), and catalase (CAT) in water dropwort leaves increased by 20.1%–27.2%, 19.2%–25.0%, 7.3%–17.0%, 15.6%–27.7%, and 10.3%–18.1%, respectively, under salt stress, whereas after acclimation, these increases were 29.8%–37.8%, 33.9%–39.1%, 27.9%–32.3%, 28.5%–37.4%, and 28.0%–33.7%, respectively. The K⁺/Na⁺ ratios in both leaves and roots of water dropwort significantly decreased by 67.5%–97.5% and 76.8%–93.8%, respectively, under salt stress, but decreased only by 39.4%–89.7% and 40.9%–82.7%, respectively, after acclimation. In conclusion, low salt stress negatively affects watercress growth and its physiological and biochemical responses, but short-term domestication ameliorates the effects of salt stress.