This study investigates the influence of synthesis conditions of iron(II) oxalate particles on the particle morphology for their utilization in smart materials known as electrorheological (ER) fluids. Particle morphology has a significant impact on the ER behavior of the particles enabling their use in many unique practical applications. In this study, fifteen various iron(II) oxalate particles differing in synthesis conditions were prepared, out of which four variations were selected for an in depth investigation due to their promising morphology. The influence of synthesis conditions on the morphology of the resulted particles was evaluated by scanning electron microscopy analysis. An X-ray diffraction analysis was employed to confirm the dominant FeC2O4 · H2O phase presented in the synthesized particles. The ER suspensions consisted of the selected four iron(II) oxalate particles dispersed in silicone oil. An optical microscope and a rheometer, both operating under external electric field, enabled a precise and accurate investigation of the structure, the ER performance. Visual observation was used to evaluate the sedimentation stability of the suspension.