Reducing the fat used in muffin production is necessary to produce muffins with low-fat content without changing physical characteristics. This reduction can be achieved by adding ingredients with high fiber content, such as soursop. This study aims to obtain the optimum concentration of soursop puree and margarine to produce muffins with the best texture, pore size, moisture content, and lowest fat content. The method used in this study is the Response Surface Methodology with the Central Composite Design using two factors, the concentration of soursop puree and margarine. The optimum treatment results obtained were the concentration of 16.159% soursop puree and 27.391% margarine with a hardness response of 3.390 ± 0.144 N, a pore size of 0.529 ± 0.046 mm2, a fat content of 8.302 ± 0.328%, and moisture content of 33.269 ± 0.397%. The optimum muffins have fat content, fiber content, carbohydrate content, hardness, pore size, reddish, yellowish, and taste attributes that are significantly different from control muffins. In contrast moisture content, ash content, protein content, volume expansion, baking loss, density, brightness, attributes of color, aroma, texture, pores, and overall were not significantly different from the control muffins. Keywords: margarine, muffin, optimization, soursop puree