Human factors are of paramount importance to the success of projects. Although a lot of studies have been carried out on human factors in project management, not much research has been done on emotional intelligence (EI). Studies have shown that EI is beneficial to both the individual and the organization. The benefits of EI to project management were investigated in terms of the style of leadership. The study was conducted in Thailand by interviewing project managers and engineers (PMEs); and client representatives. The results showed that EI affected leadership behavior of the project leader. PMEs with higher EI tend to use open communication and proactive leadership styles. It is also found that EI generates delegating, open communication, and proactive behavior, which can bring positive outcomes to the organization.