Atmospheric densities and viscosities of ionic liquids, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(6)C(1)Im][Tf2N]) and 1-hexyl-3-methylimidazolium chloride ([C(6)C(1)Im][Cl]), were measured with a Stabinger viscometer at temperatures from (293 to 373) K. High-pressure densities (p <= 200 MPa) for [C(6)C(1)Im][Tf2N] and [C(6)C(1)Im][Cl] were measured with a bellows type apparatus at temperatures from (312 to 452) K. Samples were analyzed for the water and 1-methylimidazole content before and after the measurements. For [C(6)C(1)Im][Tf2N], combined expanded uncertainties were estimated to be (1.0 and 1.8) kg.m(-3) for atmospheric and high-pressure density, respectively, and 0.85 % for viscosity. For [C(6)C(1)Im][Cl], combined expanded uncertainties were estimated to be (1.1 and 2.5) kg.m(-3) for atmospheric and high-pressure density, respectively, and 1.59 % for viscosity. The measured densities and viscosities of [C(6)C(1)Im][Tf2N] in this work agreed with some of the available literature values within their experimental uncertainties. The effect of colored impurities and the source of sample on densities and viscosities of [C(6)C(1)Im][Cl] were determined to be less than the experimental uncertainties. The [C(6)C(1)Im][Tf2N] did not decompose over the full temperature range during the measurements, while [C(6)C(1)Im][Cl] decomposed at temperatures greater than 392 K.