In the last few decades, the geographic distribution and frequency of harmful algal blooms (HABs) have been increasing worldwide, and have resulted in severe economic losses and ecological disaster. There has been a scientific consensus that there is a positive relationship between occurrences of HABs and increased eutrophication due to human activities in coastal waters. Studies demonstrated that urea has seen wide use in agriculture as a major nitrogen fertilizer in recent years, and consequently, concentrations of urea in aquatic environments have increased dramatically, becoming an important component of dissolved organic nitrogen (DON) in coastal waters. Other studies demonstrated the presence of a positive correlation between the increased input of urea into coastal waters and HABs frequencies. However, the ecological role of urea in triggering HABs, and the mechanism by which it does so (in a species-specific and physiological context in particular), are still unclear. The armored dinoflagellate Prorocentrum donghaiense is a representative HABs-causing alga found in the southeastern coastal waters of China, and has caused serious damage to fisheries and aquaculture facilities, and threatened coastal aquatic ecosystems. This species has shown a wide range of tolerance to light, temperature, and salinity, and is capable of utilizing both inorganic (NO₃^- and NH₄⁺) and organic (e.g. urea and amino acids) forms of nitrogen (N). Based on our prior study, in which we demonstrated that P. donghaiense exhibits a higher growth rate when grown in media containing urea as the sole N source, compared to those grown with NO₃^- as the N source, we investigated the effects of environmental factors (temperature, light intensity, and salinity) on the growth of P. donghaiense, and further explored the potential regulating effects of these factors and different forms of N on the activity of urease, a key enzyme involved in the metabolism of urea. The optimal temperatures for P. donghaiense growth were between 20 and 25℃, while the highest urease activity was observed at 25℃. Light was observed to significantly influence urease activity: high urease activity (9.405 fmol h^-1 cell^-1) was observed even at lower irradiance levels (< 2 μmol m^-2 s^-1), where the cell density was the lowest. Compared to light and temperature, salinity had the smallest impact on growth and urease activity, i.e., both relatively high growth rates and urease activity were measured at salinities ranging from 20 to 40 psu. Regarding the different effects of different nitrogen resources, P. donghaiense was capable of using all forms of nitrogen provided: NO₃^-, NH₄⁺, and urea, to meet its growth requirement. However, urease activity, was significantly inhibited by NH₄⁺ and NO₃^-, but enhanced by the presence of elevated concentrations of urea. More specifically, P. donghaiense exhibited the strongest urease activity three days after inoculation in the urea treatment group, while, in contrast, urease activity in media with NH₄⁺ or NO₃^- as the sole N source did not change significantly over time and was significantly lower than that observed in the urea-augmented medium. Moreover, we found that NH₄⁺ had a stronger inhibitory effect on the urease activity of P. donghaiense than NO₃^-. In the N source conversion experiments, urease activity in the NH₄⁺ substrate was still lower than that in NO₃^- substrate after the addition of equal amount of urea. In addition, urease activity was significantly elevated when ambient nitrogen was deficient. The response of P. donghaiense urease activity and growth rates to the temperature, light, salinity, and nutrient differences observed in this study may reflect an ecological adaptation of P. donghaiense, which allows it to make use of organic nitrogen when inorganic nitrogen sources are insufficient, providing P. donghaiense with a competitive advantage over co-occurring phytoplankton species when the availability of urea is higher than inorganic forms of nitrogen.