eHealth interventions can be effective in treating health problems. However, adoption in inpatient routine care seems limited. The present study therefore aimed to investigate barriers and facilitators to acceptance of eHealth interventions and of online aftercare in particular in health professionals of inpatient treatment. A total of 152 out of 287 health professionals of various professional groups in four inpatient rehabilitation facilities filled out a self-administered web-based questionnaire (response rate: 53%); 128 individuals were eligible for further data analysis. Acceptance and possible predictors were investigated with a complex research model based on the Unified Theory of Acceptance and Use of Technology. Acceptance of eHealth interventions was rather low (M = 2.47, SD = 0.98); however, acceptance of online aftercare was moderate (M = 3.08, SD = 0.96, t(127) = 8.22, p < .001), and eHealth literacy was elevated. Social influence, performance expectancy, and treatment-related internet and mobile use significantly predicted overall acceptance. No differences were found between professional and age groups. Although acceptance of eHealth interventions was limited in health professionals of inpatient treatment, moderate acceptance of online aftercare for work-related stress implies a basis for future implementation. Tailored eHealth education addressing misconceptions about inferiority and incongruity with conventional treatment considering the systemic aspect of acceptance formation are needed.