In　the　present　work　the　creep　properties　of　Sn37Pb-　and　Sn0.7Cu-based　composite　solders　reinforced　with　metallic　nano-　and　microsized　Cu　and　Ag　particles　have　been　studied.　First,　a　series　of　volume　percentages　of　reinforcements　were　selected　to　optimize　the　content　of　reinforcing　particles.　Then,　the　composite　solder　with　optimum　volume　fraction　of　reinforcement　particles,　corresponding　to　the　maximum　creep　rupture　lifetime,　was　selected　to　investigate　the　effect　of　applied　stress　and　temperature　on　the　creep　rupture　lifetime　of　the　composite　solder　joints.　In　the　creep　rupture　lifetime　test,　small　single-lap　tensile-shear　joints　were　adopted.　The　results　indicate　that　composite　solders　reinforced　with　microsized　particles　exhibit　better　creep　strengthening　than　composite　solders　reinforced　with　nanosized　particles,　although　the　mechanical　tensile　shear　strength　of　composite　solder　joints　reinforced　with　nanosized　particles　may　be　higher　than　those　reinforced　with　microsized　particles.　Moreover,　the　creep　strengthening　action　of　the　reinforcement　particles　is　more　obvious　under　conditions　of　lower　applied　stress　or　lower　test　temperature.　Strengthening　by　metallic　Cu　or　Ag　reinforcement　particles　decreases　with　increasing　temperature　or　applied　stress.　The　Sn0.7Cu-based　composite　solder　reinforced　with　microsized　Ag　particles　is　a　low-cost　lead-free　solder　that　is　easy　to　process　and　may　have　good　market　potential.