Modified mung bean starch and maltodextrin were used as a fat substitute in low-fat ice cream. The formulation of low-fat ice cream was optimized using response surface methodology (RSM) based on central composite design (CCD). The responses were overrun, melting rate, first dripping time and slurry viscosity. The results showed that incorporation of 1.5% modified mung bean starch and 2.0% maltodextrin gave a better product, whose overrun, melting rate, initial melting time and slurry viscosity of 61.7%, 20.0%, 1 249 s and 1 243 mPa·s, respectively. Texture profile analysis (TPA) showed that the hardness, adhesiveness, gumminess and chewiness of the ice cream were (811.4 ± 4.4) g, (215.7 ± 2.5) g·s, 1.091 ± 0.025 and (168.2 ± 5.6) g, respectively. The use of fat substitute significantly improved texture characteristics of ice cream. The results of size distribution showed that the D (4,3), D (10), D (50) and D (90) of low-fat ice cream increased to (3.36 ± 0.39), (0.14 ± 0.00), (0.51 ± 0.00) and (9.84 ± 1.07) μm as compared with the blank sample. This fat substitute could increase fat instability in ice cream, facilitating the formation of ice crystals. Stereo microscope showed that low-fat ice cream contained a large number of air bubbles uniform in size and evenly distributed.