Abstract. The Taguchi Design of Experiments (DOE) is a powerful statistical tool designed to identify optimal conditions in processes with efficiency and precision. By systematically reducing variability and determining the most influential factors, Taguchi DOE minimizes the number of experimental runs required while maximizing insights into process behavior. This study leverages the advantages of Taguchi DOE to optimize soap formulation using waste oil, a sustainable and eco-friendly resource. The research aims to determine the optimum parameters for soap production by analyzing key input variables: water, NaOH, waste oil, and agarwood dust. Output parameters include pH, foaming rate, antimicrobial activity, and sensory evaluation via a hedonic test, assessing appearance, aroma, texture, color, and overall impression. Taguchi analysis effectively identifies the rank order of factors influencing soap quality, with waste oil emerging as the most significant, followed by agarwood dust, water, and NaOH. The optimized formulation incorporates coconut oil, 70 ml of water, 2 g of agarwood dust, and 15 g of NaOH. Additionally, the study provides a detailed analysis of the soap’s properties and a regression model to validate its performance. By enhancing soap quality and promoting waste oil utilization, this work underscores the efficiency of Taguchi DOE in product optimization while advancing environmental sustainability goals.