The orthorhombic compound YBa2Cu3O6.7F0.3 noted F-(123) is obtained by chemical addition of 0.3 fluorine atom into the pure (123) compound with 6.7 oxygen atoms. The high pressure study by neutron powder diffraction at low temperature leads to volumic expansion coefficients at 295 K alpha(v) = 43 and 47 x 10(-6) K-1 under ambient and 4.9 kbar pressures respectively, a compressibility coefficient chi(v) = 5.4 X 10(-12) Pa-1, i.e. a bulk modulus B = chi(v)-1 = 187 GPa. These values are close to those still found for the pure (123) but disagree with other ones from the literature. The value 2.9 +/- 0.6 is found for the mean Gruneisen coefficient. It is abnormally high and far from the value 1.2 found for the bismuth cuprate (2212). The origin of this observed anomaly is discussed.