Multicomponent metal oxides have shown the potential to be excellent catalysts mainly because of synergistic interactions between the active sites. We report (Co, Mg, Ni, Cu, Zn)1-xCaxO (x = 0.05, 0.1) high entropy oxide (HEO) photocatalyst with single phase rocksalt structure (space group Fm3¯m) synthesized by solution combustion synthesis (SCS) technique. HEOs contain elements with varying electronegativities and crystal field splitting and thus exhibit a relatively lower band gap when compared to the individual constituent oxides. Adding Ca2+ results in increased covalency due to the greater exchange interaction between O 2p and transition metal (TM) 3d orbital, engendering further reduction in band gap and consequently improving photocatalytic activity in the visible region. In addition, the introduction of point defects, mainly metal/oxygen vacancy, to accommodate the larger size Ca2+ cation also contributed to the catalytic activity. The photocatalytic activity enhancement is demonstrated by visible light-assisted photodegradation of methylene blue (MB). The MB dye degradation rate constant for (Co, Ni, Cu, Zn, Mg)0.9Ca0.1O catalyst was found to be ∼0.0445 min−1, which was about six times faster than that of the pristine (Co, Mg, Ni, Cu, Zn)O.