Recently insulator-metal transition in Pr0.7Ca0.3MnO3 was observed at P = 0.5 GPa, implying a change in magnetic ground state, which was initially a pseudo-CE AFM one. In later ND study of powder sample a suppression of (1 0 1/2) AFM peak intensity was observed at high pressure. Due to a limited d-spacing range available in high pressure experiment, several scenarios of magnetic structure evolution are possible and they can be distinguished only with additional experiment over larger accessible d-spacing range. In Pr0.5Ca0.5MnO3 a rapid decrease of charge ordering (CO) temperature under pressure is observed, implying instability of initial CO CE-type AFM state. To study accurately evolution of magnetic states in Pr1-xCaxMnO3 (x=0.3, 0.5) and its correlation with structural parameters behavior , we propose to perform high pressure experiments at GEM with sapphire anvil pressure cell.