Nursing assistants can work without a professional certification to help registered nurses and licensed practical nurses. Nursing assistants engage in various tasks, e.g., washing laundry, cleaning up, and clerk tasks regarding nursing. Enhancing work motivation among nursing assistants is essential for every hospital, because when nursing assistants do their jobs well, it allows registered nurses and licensed practical nurses to complete their own specialized jobs. We examined the predictors significantly associated with nursing assistants' work motivation. For those predictors, we produced items to examine job satisfaction. Those items are classified into intrinsic and extrinsic facets. The subjects for this study were Japanese nursing assistants working in 26 hospitals with 62-376 beds (4 public and 22 private hospitals). A total of 516 nursing assistants were analyzed, with the average age and standard deviation of 42.7 ± 12.9 years; the age of 456 female subjects was 43.8 ± 12.7 years and that of 60 male subjects was 34.3 ± 11.0 years. Our results show that "work motivation" is significantly associated with "free time to do one's own things," "nursing assistants as important partners on the job," "feeling helpful to patients," "participating in decision making," and "job-skill improvement." Free time to do one's own things is an extrinsic item. Hospital administrators must monitor the workload and their quality of life among nursing assistants. All the other significant items are intrinsic. Nursing assistants are not only motivated by money. They highly value the intrinsic nature and experience of their jobs.