Co3O4　nanoparticles　were　synthesized　by　a　green　synthesis　method　using　bread　fungus　and　cobalt　nitrate　hexahydrate　as　the　precursors.　The　effects　of　the　calcination　temperature　on　the　structure　and　properties　of　nanoparticles,　and　the　ambient　temperature　on　the　photocatalytic　reaction　are　discussed.　The　cubic　structure　of　Co3O4　nanoparticles　was　obtained,　and　the　grain　size　was　between　14　and　19　nm　at　different　calcination　temperatures.　Co3O4　calcined　at　500°C　shows　good　photocatalytic　performance.　Without　adding　any　sacrificial　agent　and　cocatalyst,　the　amount　of　hydrogen　and　oxygen　released　in　5　h　were　259.4　and　135.7　μmolg-1,　respectively.　The　results　show　that,　with　the　increase　of　ambient　temperature,　the　evolution　rate　of　hydrogen　and　oxygen　is　accelerated,　and　the　atomic　ratio　of　hydrogen　to　oxygen　is　close　to　2:1.　In　addition,　the　Co3O4　photocatalyst　has　good　stability.　Our　study　provides　an　environmentally　friendly,　low-cost,　and　efficient　method　for　the　preparation　of　cobalt　oxide　photocatalysts　with　excellent　performance.　©　2020　Society　of　Photo-Optical　Instrumentation　Engineers　(SPIE).