Ionic-liquid　gating　on　a　functional　thin　film　with　a　low　voltage　has　drawn　a　lot　of　attention　due　to　rich　chemical,　electronic,　and　magnetic　phenomena　at　the　interface.　Here,　a　key　challenge　in　quantitative　determination　of　voltage-controlled　magnetic　anisotropy　(VCMA)　in　Au/[DEME](+)[TFSI](-)/Co　field-effect　transistor　heterostructures　is　addressed.　The　magnetic　anisotropy　change　as　response　to　the　gating　voltage　is　precisely　detected　by　in　situ　electron　spin　resonance　measurements.　A　reversible　change　of　magnetic　anisotropy　up　to　219　Oe　is　achieved　with　a　low　gating　voltage　of　1.5　V　at　room　temperature,　corresponding　to　a　record　high　VCMA　coefficient　of　approximate　to　146　Oe　V-1.　Two　gating　effects,　the　electrostatic　doping　and　electrochemical　reaction,　are　distinguished　at　various　gating　voltage　regions,　as　confirmed　by　X-ray　photoelectron　spectroscopy　and　atomic　force　microscopy　experiments.　This　work　shows　a　unique　ionic-liquid-gating　system　for　strong　interfacial　magnetoelectric　coupling　with　many　practical　advantages,　paving　the　way　toward　ion-liquid-gating　spintronic/electronic　devices.