This study explores the transformative impact of gallium (Ga) doping on the structural and optical properties of tin oxide NPs synthesized using chemical and green method. The nanoparticles were synthesized at different doping concentrations of gallium (Ga-SnO2). The effects of different dopant concentration on structural and optical properties of Psidium guajava capped SnO2 nanoparticles were investigated using X-ray diffraction (XRD), Ultra Violet- Visible spectrophotometer (UV-Vis), Fourier transform infrared and photoluminescence spectroscopy (PL). The bandgap energies of Ga-SnO2NPs were estimated using Tauc’s plot. The bandgap energies were observed to decrease with introduction of gallium. Highest bandgap was obtained at 2.5% and 2.0% Ga-SnO2NPs having a bandgap value of 3.25 and 3.07 eV for capped and uncapped Ga-SnO2 respectively. Smallest bandgap was obtained at 0.5% Ga-SnO2 NPs having a bandgap value of 2.29 and 2.46 eV for capped and uncapped Ga-SnO2 respectively. Fourier transform infrared spectroscopy showed the stretching vibration of SnO2 between 690–790 cm-1 wavenumbers. Structural analysis using X-ray diffraction (XRD revealed Ga doping significantly leads to a decrease in crystallite size calculated using Scherrer equation. The results obtained showed that both capped and uncapped Ga-SnO2 maintained the tetragonal rutile structure. This showed that the dopant occupied the interstitial site of the precursor materials. Derby Scherrer formula was used to calculate the crystallite size, the results obtained showed that capping agents and doping reduces the crystallite size of nanoparticles. All nanoparticles formed were in the range of 10.99–18.00 nm. The PL spectrum showed emission at a near band emission and deep level emission.