We present our study of Ca substituted hexaborides, Eu1-xCaxB6 (x=0.3, 0.35, and 0.4), through temperature-dependent magnetization M(T) and isothermal magnetization M(H) measurements under high pressures (0⩽p⩽10kbar) and magnetic fields (0⩽H⩽7T). TC of x = 0.3 increases with increasing pressure and the ferromagnetic interaction is observed to be increased in M(H). The antiferromagnetic transition behavior seen in x=0.4 at ambient pressure is gradually weakened with increasing pressure and completely subdued at p=10kbar. From these results, we found that the physical properties of Eu1-xCaxB6 are dominated by the effective magnetic interaction between Eu moments.