In a continuous search for an essential antidiabetic agent, Sida cordifolia hydroalcoholic (SCHA) extract-loaded chitosan nanoparticles (SCHA-CS-NP) were optimized. The Box–Behnken design (BBD Design-Expert software, version 14) with three parameters was used to optimize the nanoparticles after creating them using the ion gelation method. The chitosan and Tween 20 contents and the stirring speed were chosen as the independent variables, and their separate and combined effects on particle size (Y1), polydispersity index (Y2) and entrapment efficiency (Y3) were observed. The optimized formulation showed a particle size of 51 nm, an entrapment efficiency of 84.54% and a polydispersity index of 0.391. Physicochemical characterization, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), a drug release study, an ex vivo permeation study, and an antioxidant study were performed. Confocal laser scanning microscopy (CLSM) images demonstrated that chitosan nanoparticles loaded with rhodamine B-laden SCHA extract had superior penetration compared to the control (rhodamine B solution). Furthermore, compared to conventional ascorbic acid (IC₅₀ = 45 µg/mL), a superior antioxidant activity was discovered for SCHA-CS-NPs (IC₅₀ = 86.45 ± 2.24 µg/mL), while SCHA-CS-NPs also exhibited strong antidiabetic potential (IC₅₀ = 93.71 ± 1.79 µg/mL) compared to standard acarbose (IC₅₀ = 97.25 ± 1.43 µg/mL). The overall results demonstrated that SCHA-CS-NPs are a promising and efficient formulation for oral delivery.