In the present experimental study, an eco-friendly process (synthesized from rice plant source) was used to produce silica nanoparticles. Silica nanoparticles are environmentally friendly nanoparticles that have high heat transfer potential due to its abundant natural resources, low cost synthesis and mass production. The surface and atomic structure of the nanoparticles have been investigated through SEM and FTIR tests. After production of nanoparticles, water/silica nanofluid samples were prepared using two-step method that called eco-friendly nanofluid. Stability and thermal conductivity of the eco-friendly nanofluid were examined. Investigating the stability of the prepared samples, the DLS and TEM tests have been conducted as well as periodic visual observation of possible sedimentation over a period of six months through photography. The stability results indicated that the prepared samples possess excellent nano-structure and it showed long-time stability even after six months of preparation. The thermal conductivity measurement of the samples has been done in different temperatures ranging from 25 to 55 °C and solid volume fractions of 0.1, 0.25, 0.5, 1, 1.5, 2, 2.5, and 3%. The results showed the maximum thermal conductivity enhancement of 38.2% which took place at the temperature of 55 °C and solid volume fraction of 3%. Moreover, new precise correlation to predict the thermal conductivity of the eco-friendly nanofluid has been proposed with the maximum deviation of 2.72%. Finally, according to the results, it can be claimed that synthesis of environmentally friendly nanoparticles of silicon oxide with a plant source for nanofluid production is important, and this type of nanofluid can be introduced as an environmentally friendly alternative fluid with high heat transfer potential in thermal systems.