Objective: In this study, a quality-by-design (QbD) approach was used to develop a betamethasone suspension for injection formulation and to investigate the possible effects of formulation and process variables on the critical quality attributes (CQAs) of the formulation. Material and Method: It was determined that the CQAs of the formulation were particle size distribution, viscosity, sedimentation time, density and assay of active substances and preservatives, considering the quality target product profile (QTPP). Potential risk factors that may affect the CQAs of the formulation were identified using an Ishikawa diagram, and a six-factor, two-level Plackett-Burman experimental design was used to statistically investigate the effects of selected formulation and process variables. The prepared formulations were tested, and variance and multiple linear regression analyses were performed with the acquired data. Result and Discussion: As a result of the one-way analyses of variance (ANOVA) and multiple linear regression analyses, the established statistical models for the assay of methyl parahydroxybenzoate and propyl parahydroxybenzoate, and viscosity were found to be significant, the established models for other independent variables were not significant. The concentration of carmellose calcium and filter type was found to be the most significant formulation and process variables. In conclusion, this study showed that understanding the formulation and process variables that may affect the CQAs of injectable suspension formulations with a QbD approach could be useful for formulation development and optimization.