One-part　geopolymers　are　a　greener　alternative　to　Portland　cement　and　are　more　suitable　in　engineering　applications　compared　with　two-part　geopolymers.　The　effects　of　mechanical　activation　on　the　properties　and　the　mechanism　of　the　pozzolanic　reaction　of　fly　ash　(FA)/slag-based　geopolymer　paste　prepared　using　the　one-part　method　were　studied.　Simple　mixing　was　used　for　the　control　group　and　the　effect　of　mechanical　activation　on　the　macroscopic　properties　of　geopolymers　was　studied　using　tests　for　compressive　strength,　fluidity　and　setting　times.　The　effect　of　mechanical　activation　on　the　pozzolanic　reaction　of　geopolymers　was　assessed　using　isothermal　calorimetry,　X-ray　diffraction,　Fourier　transform　infrared　spectroscopy　and　thermogravimetric　analysis.　The　results　showed　that　the　28-day　compressive　strength　of　the　geopolymer　formed　by　mechanical　activation　was　26%　higher　than　that　of　the　geopolymer　prepared　using　simple　mixing.　Workability　and　fluidity　were　also　enhanced.　The　reactivity　of　the　precursor　was　improved　by　mechanical　activation,　particularly　for　the　FA.　The　mechanically　activated　FA　experienced　a　pozzolanic　reaction　within　7　days,　while　the　undisturbed　FA　produced　pozzolanic　activity　after　14-28　days.　In　addition,　mechanical　activation　lessened　the　carbonisation　of　the　one-part　FA/slag-based　geopolymer　The　implications　of　these　results　in　terms　of　the　influence　of　mechanical　activation　on　pozzolanic　activity　are　discussed.