This　study　examines　the　impact　of　social　trust,　the　state　ownership　and　their　joint　effects　on　investment　efficiency　in　China　using　6885　firm-year　observations　from　2010　to　2018.　We　find　that　higher　social　trust　is　associated　with　higher　investment　efficiency,　and　the　state　ownership　leads　to　lower　investment　efficiency.　The　SOEs　exhibit　higher　under　and　over-investment　problems　relative　to　non-SOEs.　The　lower　investment　efficiency　of　SOEs　is　further　amplified　in　provinces　with　higher　social　trust.　These　findings　are　consistent　with　agency　and　information　asymmetry　explanations,　and　robust　to　endogeneity　and　alternative　measurement　of　variables.