Stable nanofluid detergents containing ZnO, palm oil-based primary alkyl sulfates (palmPAS) surfactant, and carboxymethyl cellulose (CMC) have been synthesized and the Influence of CMC composition on its stability and detergency have been studied. Stability test was studied by sedimentation method and detergency test was studied by stain removal test and stain degradation test. Both stain removal test procedure and stain degradation test were similar to regular washing process. A light source was added during washing process for stain degradation test. Nanofluid detergents showed increased stability and decreased detergency with increasing CMC concentration. Detergency were improved by photocatalytic degradation of stains by ZnO nanoparticles under light irradiation. The optimum CMC concentration that meets Indonesian National Standard (SNI) was 6 wt%. The nanofluid detergent showed homogeneous phase after 14 days indicating good stability. On the other hand, detergency decreased from 87% to 76% in stain removal test and 90% to 84% in stain degradation test compared to the nanofluid detergent with no added CMC.