This　study　assesses　the　punching　shear　characteristics　of　ultra-high-performance　concrete　(UHPC)　slabs　in　two　phases.　The　initial　phase　involved　experimental　tests　to　determine　the　critical　thickness　differentiating　punching　shear　failure　and　flexural　failure　modes.　Subsequently,　the　second　phase　further　explored　the　punching　shear　behavior　of　UHPC　slabs　by　analyzing　various　key　parameters.　The　experimental　findings　indicated　that　as　the　thickness　of　the　slabs　increased,　the　punching　shear　capacity　exhibited　nearly　linear　enhancement,　surpassing　the　improvement　seen　in　bending　capacity.　Thus,　a　critical　thickness　of　at　least　100　mm　was　identified　as　the　threshold　distinguishing　punching　shear　failure　from　flexural　failure.　Additionally,　an　increase　in　slab　thickness　significantly　elevated　the　cracking　load　of　the　UHPC　slabs.　While　a　higher　reinforcement　ratio　of　3.5%　slightly　increased　the　first　cracking　load,　it　greatly　enhanced　the　ultimate　capacity.　The　addition　of　steel　fibers　also　contributed　to　improvements　in　both　cracking　and　ultimate　loads,　albeit　to　a　limited　extent.　The　use　of　a　granite　powder　substitute,　comprising　10%　of　the　mass　of　silica　fume,　had　minimal　impact　on　the　punching　shear　capacity　of　the　UHPC　slabs.　Finally,　a　comparison　is　drawn　between　the　experimental　results　for　punching　shear　capacity　and　those　obtained　from　various　theoretical　models.　This　comparison　highlights　significant　discrepancies　in　the　results,　stemming　from　the　differing　parameters　employed　in　the　proposed　theoretical　models.　Among　the　prediction　models,　the　JSCE　model　provided　the　most　balanced　and　conservatively　accurate　estimation　of　punching　shear　capacity,　effectively　incorporating　the　effects　of　slab　thickness,　reinforcement　ratio,　and　fiber　content,　thus　highlighting　its　potential　as　a　reliable　reference　for　future　design　recommendations.　This　information　will　serve　as　a　valuable　reference　for　future　research　and　practical　applications　related　to　UHPC　bridge　decks　and　slabs.　©　2025　by　the　authors.