Response surface methodology (RSM) was used to optimize solid– liquid ultrasonic-assisted extraction (UAE) conditions for the maximization of the stigmasterol content from an Ayurvedic plant Tecomella undulata (T. undulata) bark. The Box—Behnken design (BBD), form of RSM, was employed for the optimization of ultrasonic extraction parameters, viz., temperature (°C), drug-to-solvent ratio (mg/10 mL), and time (min). Quantification of stigmasterol was performed using high-performance thin-layer chromatography in visible range (HPTLC–vis). HPTLC analysis of stigmasterol was carried out in the absorbance mode at 510 nm using toluene—ethyl acetate—formic acid (8.0:1.5:0.5, v/v) as the solvent system. This system was found to give compact spots for stigmasterol at Rf 0.44 ± 0.01. The optimal UAE processing parameters were the following: extraction time, 46 min; temperature, 50°C; and drug-to-solvent ratio, 528 mg/10 mL, with stigmasterol yield of 2.45 ± 0.073%. This study proves that the use of BBD for the optimization of UAE process provides more accuracy than single factorial optimization. The optimized UAE was a more efficient technique over conventional Soxhlet extraction (CSE) due to the higher stigmasterol content along with the low ingredient and time consumption. To the best of the authors’ knowledge, no studies have been published previously addressing specifically the optimization of ultrasonic extraction of stigmasterol from T. undulata bark using BBD.