In　the　present　work,　the　creep　strain　of　the　composite　solder　joint　is　measured　using　a　stepped　load　creep　test　on　a　single　specimen.　Based　on　the　creep　strain　tests,　constitutive　relations　for　the　steady-state　creep　rate　are　determined　for　the　Ag-particle-reinforced　Sn-0.7Cu-based　composite　solder　joint.　In　addition,　creep　strain　tests　on　the　Sn-0.7Cu　solder　joint　are　performed　as　a　comparison.　It　is　found　that　the　activation　energy　of　the　Ag-particle-reinforced　Sn-0.7Cu-based　composite　solder　joint　is　higher　than　that　of　the　Sn-0.7Cu　solder　joint.　At　the　same　time,　the　stress　exponent　of　the　Ag-particle-reinforced　Sn-0.7Cu-based　composite　solder　joint　is　higher　than　that　of　the　Sn-0.7Cu　solder　joint.　It　is　expected　that　the　creep　resistance　of　the　Ag-particle-reinforced　Sn-0.7Cu-based　composite　solder　joint　will　be　superior　to　that　of　the　Sn-0.7Cu　solder　joint.　Finally,　the　creep　deformation　mechanisms　of　the　solder　joint　are　discussed.