The effective thermal conductivity of three water based nanofluids (NFs) consisting of large aspect ratio fillers - carbon nanotubes (CNTs), silver nanowires, copper nanowires - were measured by transient hot wire method. The results show that silver nanofluid has the highest thermal conductivity compared with copper and CNTs nanofluids, while the latter two present almost the same thermal conductivity at the same volume fraction. The experiment indicates that particle shape has a substantial effect on the effective thermal conductivity of suspension and shape factor is one of the most important factors that leads to the large discrepancies among the experimental values of the thermal conductivities. Our results reveal that material with higher thermal conductivity is not a decisive factor and not always effective to improve the thermal transport properties of nanofluids. (C) 2013 Elsevier Ltd. All rights reserved.