Micromechanical　properties　of　a　reduced-activation　ferritic/martensitic　steel　CLF-1　were　characterized　by　nanoindentation　tests　with　Berkovich　indenter,　microhardness　tests　with　Vickers　and　Knoop　indenters,　and　microscratch　tests　with　Berkovich　and　spherical　indenters　to　investigate　the　effects　of　different　indenters.　Elastic　modulus　and　indentation　hardness　obtained　by　various　methodologies　such　as　energy-based　and　displacement-based　approaches　are　consistent　with　those　obtained　by　Oliver　&　Pharr　method.　The　reasonable　fracture　toughness　of　CLF-1　steel　can　also　be　obtained　by　energy-based　nanoindentation　method　based　on　the　deterioration　of　indentation　hardness　with　the　critical　void　volume　fraction　of　0.49.　©　2023