1,1,1,3,3-pentafluorobutane (HFC-365mfc) is currently proposed as a substitute for CFCs in several applications. Experimental data on this fluid are still not sufficient to describe accurately its thermodynamic behaviour. Liquid density is one of the most important properties required to develop precise equations of state. At the state of the art, data of compressed and saturated liquid density are lacking. In this paper density in liquid phase was measured along eight isotherms ranging from 283.15 to 343.06 K at pressures up to 25 MPa. The paper presents also correlations for the compressed liquid by means of a Tait equation and the saturated liquid density. (C) 2004 Elsevier B.V. All rights reserved.