The present study investigated possible benefits of magnesium ion (as MgCl2) in organophosphorus poisoning targeting its ability to interact with substrates and membrane enzymes. Blood samples collected from volunteered healthy adult by venepuncture into anticoagulant test tubes containing EDTA were separated into plasma and red blood cell and divided into three groups namely: normal, pesticide only (0.25‐2.0 mmol/L chlorpyrifos) and pesticide (0.25‐2.0 mmol/L chlorpyrifos) + 0.1 mol/L MgCl2. Acetylcholinesterase, Na+/K+ ATPase and Ca2+ ATPase activities were evaluated. Results showed that Chlorpyrifos significantly (P < .05) reduced the levels of cholinesterase both in plasma and on red blood cells. Red blood cells Na+/K+ ATPase and Ca2+ ATPase were also significantly (P < .05) reduced by chlorpyrifos while MgCl2 counteracted effects of chlorpyrifos with significant (P < .05) increase in the levels of cholinesterase, Na+/K+ ATPase and Ca2+ ATPase. We concluded that MgCl2 neutralized effects of chlorpyrifos by promoting normal ATPase activities and inhibiting release of acetylcholine from cell.