In this paper, isochoric p rho Tx and specific heat capacity c(v) for (R1234yf+ R290) binary mixtures were measured using an adiabatic batch calorimeter with intermittent heating. A total of 42 p rho Tx data points over temperatures from (254.28 to 348.30) K and 89 isochoric specific heat capacity data points over temperatures from (255.48 to 347.55) K were obtained for liquid (R1234yf + R290) with mole fractions of R1234yf at (0.825, 0.607, 0.521 and 0.285). The standard uncertainties were estimated to be 10 mK for temperature, 5 kPa for pressure, 0.3% for density and 1.0% for isochoric specific heat capacity. The experimental p rho Tx data were correlated by an empirical Tait equation with average absolute relative deviation of 0.19%. A Helmholtz energy equation of state based on the multi-fluid approximations model was developed for (R1234yf+ 8290) using the present and available experimental data. Eleven mixture rules are employed and the optimal Helmholtz energy equation of state calculates the density, VLE and isochoric specific heat capacity properties with sufficient accuracy. The compressed liquid density and isochoric specific heat capacity data in this work are well represented with average absolute relative deviation of 0.21% and 0.66%, respectively. (C) 2018 Elsevier Ltd.