Expansive　clay,　a　kind　of　clayey　soil,　is　widely　distributed　in　seasonally　frozen　regions.　Numerous　studies　have　attempted　to　explain　the　frost　heave　characteristics　of　clayey　soils,　but　few　of　them　have　paid　attention　to　the　frost　heave　characteristics　of　unsaturated　expansive　clay,　especially　considering　the　influence　of　swelling　properties.　In　this　study,　a　series　of　freezing　temperature　tests　and　step-freezing　tests　on　an　unsaturated　moderately　expansive　clay　and　a　silty　clay　were　conducted.　The　silty　clay　was　taken　as　a　reference.　The　testing　program,　experimental　results　are　presented　and　discussed,　especially　to　the　freezing　point,　evolution　of　temperature　in　the　specimens　at　different　elevations,　water　content　distributions　and　cryostructures　after　freezing,　frost　heave　during　freezing,　and　state　paths.　In　this　regard,　a　physico-empirical　approach　is　developed　to　obtain　the　relationship　between　freezing　point　and　initial　water　contents.　Experimental　data　show　that　the　freezing　point　of　expansive　clay　varies　greatly　with　initial　water　contents.　The　obvious　highly　exothermic　phase　change　occurs　in　expansive　clay　during　the　early　stage　of　freezing　with　penetration　decrease　lagging　behind.　The　heave　amount　of　expansive　clay　is　made　up　of　the　displacement　caused　by　increasing　water　content　in　the　unfrozen　zone　due　to　freezing-induced　water　flux　and　the　frost　heave.　The　state　paths　show　significant　variation　of　saturation　and　dry　density　of　expansive　clay　after　freezing　and　have　a　practical　advantage　of　indicating　the　extent　of　possible　expansion　while　thawing.　On　this　basis,　the　state　and　variation　of　pore　water　are　highlighted　as　the　critical　primary　factors　in　determining　the　frost　heave　characteristics　of　unsaturated　expansive　clay　in　open　system.　Overall,　this　study　further　enhances　the　understanding　of　frost　heave　characteristics　of　the　unsaturated　moderately　expansive　clay.