The aim of this study was to examine the relationship between staffing and job satisfaction of registered nurses (RNs) and nursing assistants (NAs).Although a number of previous studies have demonstrated the link between the numbers of patients cared for on the last shift and/or perceptions of staffing adequacy, we could find only one study that utilized a measure of actual staffing (opposed to perceptions of staffing adequacy) and correlated it with job satisfaction of registered nurses.This cross-sectional study included 3523 RNs and 1012 NAs in 131 patient care units. Staff were surveyed to determine job satisfaction and demographic variables. In addition, actual staffing data were collected from each of the study units.Hours per patient day was a significant positive predictor for registered nurse job satisfaction after controlling for covariates. For NAs, a lower skill mix was marginally significant with higher job satisfaction. In addition, the more work experience the NAs reported, the lower their job satisfaction.Adequate staffing levels are essential for RN job satisfaction whereas NA job satisfaction depends on the number of assistive personnel in the mix of nursing staff.Two implications are (1) providing adequate staffing is critical to maintain RN job satisfaction and (2) the NA job needs to be re-engineered to make it a more attractive and satisfying career.