In the present work, the thermal conductivity and viscosity studies of multiwalled carbon nanotubes (MWCNTs)-Dowtherm A (eutectic mixture of biphenyl (C12H10) and diphenyl oxide (C12H10O)) nanofluids-are presented considering the influence of particle weight percentage (0.001-0.005wt%) and temperature ranging from 303K to 323K. As-received MWCNTs are characterized using x-ray diffraction (XRD), FT-Raman spectroscopy, thermogravimetric analysis, and transmission electron microscopy (TEM). The suspensions consist of MWCNTs dispersed in Dowtherm A and they are stabilized by sonication. The result shows that the thermal conductivity of MWCNT-Dowtherm A nanofluids depends strongly on particle concentration and temperature which increases linearly with both the weight percentage of nanoparticles and also with that of temperature. It is also observed that the viscosity of nanofluids increases with the increase in concentration of nanoparticle and decreases with the rise in temperature. Stabilization mechanisms of dispersions are analyzed by UV-visible (Vis) spectrophotometry measurement to quantitatively characterize the colloidal stability of the MWCNT dispersions.