Nanofluids (NFs) are solid-liquid composites prepared by stabilizing nanostructured materials in a base liquid, such as water, ethylene glycol (EG) and engine oil. They have exhibited some potential to replace with conventional heat transfer fluids to enhance their thermal characteristics. NF has complex system and its thermo-physical properties including TC and viscosity can be influenced by several factors such as base liquid. The effect of base liquid on thermo-physical properties of NFs is not well studied. In this work this effect has been studied by comparing the TC and viscosity of a commercial silver (Ag) NFs with lab-made water and EG base Ag NFs. For this purpose, at first commercial water based Ag suspension with 1wt% Ag nanoparticles (NPs) was used. The original suspension was centrifuged and the obtained Ag NPs was re-dispersed in EG to prepare EG based Ag NF (1wt%). In order to study the effect of Ag NP concentration on thermo-physical properties, NFs with various concentrations (1, 1.5 and wt%) were fabricated from the original samples containing 1wt% Ag NP. For this end NFs with higher NP concentrations were fabricated by centrifuging and concentrating these samples in base liquids. Therefore, six NFs with different base liquids (water and EG) and various Ag NP concentrations (1, 1.5 and 2wt%) were prepared and studied. The physicochemical properties of Ag NP/NF were characterized by using various techniques and instruments including Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Diffraction (ED), Dynamic Light Scattering (DLS) and Fourier Transform Infrared Spectroscopy (FT-IR). Ag NP displayed an average primary particle size of 40±5 nm from SEM micrographs. The thermo-physical properties of NFs including TC and viscosity of NFs were measured at different temperatures from 20 to 40 ^oC. The Newtonian behavior was observed for NFs with both water and EG base liquids. Moreover, viscosity of all NFs was increased by increase of Ag NP concentration and decreased by increase in temperature. The TC of NFs was measured and analyzed by Transient Hot Wire (THW) method at the same temperature range. The TC tests showed increase of TC with the increase of Ag NPs concentration as well as increase in temperature. As a result and compared to the water based suspensions, NFs with EG base liquid revealed higher TC enhancement and lesser viscosity increase. EG based NFs seem to be more beneficial for heat transfer applications. Among all NFs, a maximum TC enhancement of ~12.2 % was obtained for EG based NF with 2wt% Ag NP at 40 ^oC while maximum increase in viscosity of ~ 4 % was observed for the same NF showing the capability of utilizing this NF as heat transfer fluid. Finally and in order to compare the experimental results with the estimated data, proper predictive models/correlations were applied for NFs with both water and EG base liquids and our finding are presented in detail.