Horizontal-tube falling-film heat transfer characteristics of aqueous aluminum oxide nanofluids at concentrations of , , , (with and without sodium dodecylbenzene sulfonate), and are investigated and compared with predictions developed for conventional fluids. The thermophysical properties of the nanofluids, including thermal conductivity, kinematic viscosity, and surface tension, are reported, as is the mode transition behavior of the nanofluids. The experimental results for heat transfer are in good agreement with predictions for falling-film flow and no unusual Nu enhancement was observed in the present studies. Additionally, a 20% mode transitional Reynolds number increase was recorded for transitions between sheets and jets and jet-droplet mode to droplet mode. Although the findings with water-alumina nanofluids are not encouraging with respect to heat transfer, the results extend nanofluid data to a new type of flow and may help improve our understanding of nanofluid behavior. Moreover, this work provides a basis for further work on falling-film nanofluids.