The paper examines the determinants of employee engagement in the not-for-profit organization (NFPO) sector. A structured questionnaire survey of 205 NFPO employees in Vietnam was employed, preceded by in-depth interviews with NFPO associates and managers. After a multiple regression analysis to study the impact of five independent variables on one dependent variable, the study reveals that Work design and Work-life balance are positively and significantly associated with employee engagement. Of which, Work design is measured by the level of job fit, job autonomy, job challenge, and job meaningfulness. On the other hand, Work-life balance involves measurement aspects consisting of how reasonable the workload is and organizational support. Meanwhile, different from the business world, Leadership, Learning and Development, and Recognition do not show statistically positive impacts on employee engagement in NFPOs. Still, they are crucial back-supporting factors to ensure employee experience at work. Further, the study finds that personal growth contributes a great part to keep employees in the sector motivated. This paper brings the area of study to the forefront in an effort to benefit the practice of human resources management in NFPOs as well as support employees in the sector with a higher quality working experience.