Efficiency of oxide semiconductors for photocatalytic degradation of organic pollutants is highly dependent on their morphology, particle size, electron-hole recombination and oxygen vacancies. Doping of cations modifies the phase composition and induces oxygen vacancies needed for faster photocatalytic degradation of organic contaminants. Here, thioglycerol capped undoped and noble metal (Ag and Au) doped sub-10 nm sized CeO2 nanoparticles (NPs) have been successfully synthesized at natural pH by co-precipitation method and were used as photocatalyst for degradation of rhodamine blue dye (RhB) in an aqueous medium under UV-Visible (UV-Vis.) irradiations without the addition of any external reagent. Photocatalytic studies revealed that among undoped and doped (Ag/Au) CeO2 NPs, 2.0 at% Ag and 0.4 at% Au doping concentrations are optimum to demonstrate superior degradation efficiency. Degradation time was reduced further when RhB dye has been degraded with optimum doped NPs synthesized at higher pH. Moreover, gold doped NPs have shown better photocatalytic efficacy as compared to silver doped NPs. With the help of various characterizations, a possible degradation mechanism has been proposed which shows the effect of generation of oxygen vacancies owing to the doping of Ag and Au on photodegradation process.