Objective　Metabolic　syndrome　(MetS)　has　a　high　prevalence　in　the　United　States　(US);　however,　limited　research　comprehensively　evaluates　the　relationship　between　muscle　quality　index　(MQI)　and　MetS.　This　study　aims　to　investigate　the　association　between　MQI　and　MetS.　Methods　Adults　aged　20-60　years　from　the　2011-2014　National　Health　and　Nutrition　Examination　Survey　were　included.　Handgrip　strength　(HGS)　was　measured　using　a　dynamometer,　and　appendicular　skeletal　muscle　mass　(ASM)　was　assessed　via　dual-energy　X-ray　absorptiometry.　MQI_total　was　calculated　as　the　sum　of　HGS　from　both　hands　divided　by　ASM.　Weighted　multivariable　logistic　regression　models　and　restricted　cubic　splines　(RCS)　were　used　to　explore　the　association　between　MQI_total　and　MetS,　and　subgroup,　interaction,　and　sensitivity　analyses　were　conducted.　Results　A　total　of　4,503　US　residents　were　included　in　the　study,　with　1,165　diagnosed　with　MetS,　yielding　a　prevalence　of　25.9%　(1,165/4,503).　The　weighted　multivariable　logistic　regression　model　indicated　that　after　adjusting　for　multiple　covariates,　MQI　was　negatively　associated　with　the　risk　of　MetS　(odds　ratio　[OR]　=　0.49,　95%CI:　0.32-0.73).　Among　the　different　components　of　MetS,　MQI　was　negatively　associated　with　elevated　waist　circumference　(OR　=　0.19,　95%CI:　0.12-0.28),　elevated　high-density　lipoprotein　cholesterol　(OR　=　0.66,　95%CI:　0.51-0.85),　and　elevated　serum　triglycerides　(OR　=　0.66,　95%CI:　0.51-0.85).　RCS　revealed　a　negative　linear　relationship　between　MQI　and　MetS　(P　＜　0.001,　Pnon-linear　=　0.98).　Conclusion　Low　MQI　is　associated　with　an　increased　risk　of　MetS,　exhibiting　a　linear　relationship.　These　findings　suggest　that　improving　muscle　quality　may　be　an　effective　strategy　for　the　prevention　of　MetS.