With the increasing number of people with disabilities caused by an aging global population, the need for long-term care is gradually increasing. Nursing assistants (NAs) are the primary providers of direct care services to older adults with disabilities, whose knowledge, skills, and beliefs affect the quality of care provided. This study aimed to investigate the influential factors affecting NAs’ current competences. A total of 255 NAs’ valid questionnaires were collected from 20 long-term care institutions in Taiwan through convenience sampling. The questionnaire comprised dimensions of demographics and care competence. The study results indicated that NAs had the greatest care competence in the domain of recognition of patient rights (4.64 ± 0.54 points). The multiple regression indicated that age, religion, job category, disability care experience, the receiving of performance bonuses, and the receiving of year-end bonuses significantly affected the level of care competence (p < 0.05). With the aforementioned findings, the results of this study serve as references for the government in employing long-term care NAs and developing management policies. Training programs for NAs should be developed to improve the quality of care provided to older adults with disabilities.