Hecellose is a cellulose ether product derived from wood and cotton, consisting of hydroxyethyl cellulose (HEC). It is a biologically important substance that is widely used in various industrial and everyday applications. HEC’s stability and versatility of HEC make it valuable in industries such as food, pharmaceuticals, cosmetics, construction, petrochemicals, and medical devices. Due to its wide range of applications and extensive use, concerns have arisen about the potential environmental impact and risks to human health associated with hydroxyethyl cellulose (HEC). HEC is considered a safe substance, but its primary raw material, ethylene oxide, is classified as a hazardous substance. Therefore, the toxicity of HEC was evaluated using ecotoxicological methods that involve microorganisms. In this study, nitrate-reducing microorganisms and sulfate-reducing microorganisms were utilized. The nitrate-reducing microorganisms exhibited a toxicity of over 60% after 48 hours, while the sulfate-reducing microorganisms showed a toxicity of approximately 20% after 6 hours. The difference in toxicity is believed to be attributed to variations in the duration of cultivation and factors that hinder the activity of microorganisms.