A　series　of　MgxFe3-xO4　(x　=　0-1)　nanoparticles　was　synthesized　in　order　to　prepare　novel　MgxFe3-xO4/glassy　carbon　modified　electrodes.　Effects　of　magnesium　content　(x)　on　the　analytical　performance　of　the　modified　electrodes　in　the　detection　of　gallic　acid　were　evaluated.　It　was　found　that　magnesium　concentration　and　crystallite/particle　size　of　the　prepared　nanoparticles　play　significant　roles　in　the　sensing　properties　of　modified　electrodes.　The　increase　of　magnesium　concentration　up　to　the　value　of　x　=　0.4　in　MgxFe3-xO4/glassy　carbon　paste　was　accompanied　by　an　increase　of　the　corresponding　oxidation　current　of　gallic　acid.　However,　further　growth　of　x　value　caused　decline　of　the　obtained　oxidation　current.　An　electroanalytical　procedure　was　established,　and　the　analytical　performance　of　the　proposed　Mg0.4Fe2.6O4/glassy　carbon　paste　electrode　was　monitored　using　previously　optimized　experimental　conditions.　A　working　linear　range　from　1-39　mu　M　gallic　acid　was　obtained　with　detection　limit　of　0.29　mu　M.　According　to　these　results,　the　developed　procedure　can　be　applied　for　detection　of　low　concentrations　of　gallic　acid　with　satisfactory　selectivity　in　the　presence　of　some　common　naturally　occurring　compounds.　Experimental　results　indicate　that　the　developed　procedure　could　be　a　novel　approach　in　the　detection　of　antioxidant,　overcoming　some　known　disadvantages　such　as　passivation,　and　could　be　a　promising　replacement　for　sophisticated　chromatographic　methods.