The low-temperature variations of the thermal expansion coefficient α(T) of a PrBa 2 Cu 3 O 6 + x ceramic are reported for two oxygenation states (x=0.4 and 0.9). They show a peak at the ordering temperature of Pr deduced from the susceptibility χ(T) and the specific heat C p (T), i.e. at T N =9.5 and 14.5 K, for x=0.4 and 0.9, respectively. The deduced Gruneisen parameter Γ e f f is rather large, show almost no anomaly at T N , but a sharp increase below ~5K. The origin of these variations is discussed in terms of magnetic behaviour of the Pr and Cu sublattices.