Magnetic susceptibility and magnetic hysteresis measurements were performed for rare earth pyrochlores R2Ru2O7 (R = Pr, Nd and Sm-Yb). The compounds of R = Pr, Nd, Sm and Eu show magnetic transitions at 165, 150, 135 and 120 K, respectively. Below the transition temperatures, there is a large difference in the temperature dependence of the magnetization measured under zero-field-cooled conditions (ZFC) and under held-cooled conditions (FC), but no magnetic hysteresis has been observed. These results show that below the transition temperatures, the magnetic state of these pyrochlores transforms to a spin-glass state. When the temperature is further decreased through similar to 20 K, apparent cusps have been observed for R = Nd, Sm and Eu in the susceptibility-temperature curves. Magnetic hysteresis measurements at 5.0 K indicate that there is a possibility of a contribution of weak ferromagnetism to the magnetic behaviour of Sm2Ru2O7 at very low temperatures. That is, at these very low temperatures, both the spin-glass state and a weak ferromagnetic state may coexist for Sm2Ru2O7.