This paper reports the photocatalytic efficacy of green-synthesized silver nanoparticles. The synthesis of silver nanoparticles using the leaf extract of Ocimum tenuiflorum is demonstrated. Silver nanoparticles with an average size of approximately 25–30 nm were synthesized at room temperature. The nanoparticles suspended in solution remained stable for over 50 days. The photocatalytic behavior of these Ag nanoparticles was evaluated through the degradation of Rhodamine B dye. Photodegradation studies revealed that the green-synthesized Ag nanoparticles effectively degraded Rhodamine B dye in the concentration range of 10 µmol/L to 30 µmol/L under direct sunlight. It was observed that the nanofluid containing Ag nanoparticles with sizes between 25–30 nm exhibited the highest stability and photocatalytic degradation efficiency, with a rate constant of 2.43 × 10⁻³ min⁻¹ under sunlight irradiation.