The viscosity, density, and electrical conductivity of 1-hexyl-3-methylimidazolium bis(trifluorosulfonyl)imide have been measured at temperatures from (288 to 433) K and at pressures up to 50 MPa. A vibrating wire viscometer was used for the measurements of viscosity that have an expanded uncertainty (k = 2) of +/- 2 %. The density was obtained from a vibrating tube densimeter with an expanded uncertainty (k = 2) of +/- 0.3 %. The electrical conductivity K(f ->infinity) was determined from impedance measurements at frequencies in the range (0.5 to 10) kHz with an expanded (k = 2) uncertainty of 2 %. All measurements were conducted with a sample distributed by NIST as part of an IUPAC project. The water mass fraction was determined before and after the measurements. The viscosity and density of a sample with initial water content of 7 center dot 10(-6) were represented by interpolating expressions with standard deviations of 0.4 % and 0.03 %, respectively. Differences between the experimental and calculated values are comparable with the expanded (k = 2) uncertainties. For temperatures that overlap the temperature range (288 to 433) K at p = 0.1 MPa, literature values of density differ by <= +/- 0.2 % while the reported viscosities differ by <= +/- 7 % from these empirical representations of the measurements. There are no values of the viscosity at p > 0. 1 MPa reported in the literature to compare our results. At p > 0. 1 MPa, the literature values for density reported by Gomes de Azevedo (J. Chem. Thermodyn. 2005, 37, 888-899) deviate from our smoothing equation by less than -0.2 % at temperatures and pressure that overlap ours. The electrical conductivity was determined on a sample with initial water mass fraction of 90 center dot 10(-6). The results were represented within the expanded uncertainty by an empirical function against which the literature values differed by no more than +/- 5 %.