People have long used plants and plant-derived products to treat a wide range of illnesses. In the present work, Tecoma stans flower was extracted using 90% ethanol. Flavonoids and total phenolic constituents of T. stans flower extract were screened, and polyphenolic compounds were assessed using high-performance liquid chromatography (HPLC). Anti-diabetic via α-amylase and α-glucosidase assays, antioxidant via 2,2-diphenyl-1-picryl-hydrazyl-hydrate, ferric reducing antioxidant power, and total antioxidant capacity of T. stans flower extract were assessed. The cytotoxic action for T. stans flower extract was assessed versus WI-38 (human fetal lung fibroblast cells), PC3 (prostate cancer cell line), and SK-OV3 (ovarian cancer cell line). The T. stans extract showed promising in vitro anti-diabetic effect with IC50 = 12.08 ± 0.2 µg/mL and 22.83 ± 0.3 µg/mL for α-amylase and α-glucosidase, respectively. Moreover, T. stans showed good in vitro antioxidant action with IC50= 5.36 ± 0.2 µg/mL for DPPH testing, and the best antitumor impact versus PC3 cells with IC50 = 113.27 ± 1.59 µg/mL. Flow cytometric analysis confirmed the role of T. stans in acceleration in apoptosis of PC3 cells through regulation of oxidative enzymes. These results indicate that the derived materials from T. stans flower have multiple medicinal applications.