This study presents an exploratory investigation of SMEs in Vietnam to understand the impact of personal-level factors on middle managers’ work motivation and the moderating role of work environment. A survey of 450 middle managers (MMs) in 150 Hanoi’s SMEs was conducted. The findings of this research showed a significant positive impact of Achievement (ACHV), Recognition (RECOG), and Responsibility (RESP) on work motivation of MMs under the investigation. Furthermore, the result indicated that the work environment affects the relationship between personal-level factors and work motivation of participants. Consequently, both work environment improvement and strategies related to personal-level factors need to be taken into consideration. Especially, Recognition and transparency in Responsibility are appreciated in organizations with a low level of work environment satisfaction. However, there were no indications that Participation (PAR) and Communication (CMM) have a considerable impact on work motivation of respondents, being neither low level nor high level of work environment satisfaction. Based on the findings, recommendations are suggested for Vietnam’s SMEs to improve work motivation of MMs, by (i) developing standards with emphasis on their achievement, (ii) paying attention to organizational culture focusing on the responsibility of this managerial level, and (iii) building an adequate incentive system, especially non-financial incentives.