Background Metabolic syndrome (MetS) is common in older adults and is associated with cardiovascular disease, type 2 diabetes, and functional decline. In Vietnam, evidence on MetS in older adults is scattered across community- and hospital-based studies, and prevalence estimates may vary substantially depending on the diagnostic criteria used.Objectives To synthesise the available evidence on the prevalence of MetS and associated factors among older adults in Vietnam, with stratification by NCEP-ATP III and IDF criteria.Methods A systematic review and meta-analysis of observational studies was conducted using PubMed, Scopus, and manual searches of Vietnamese journals and institutional repositories through 12 April 2026. Eligible studies were conducted in Vietnam, included participants aged 60 years or older or extractable elderly subgroup data, and reported MetS prevalence and/or associated factors using NCEP-ATP III, modified NCEP-ATP III, harmonised, or IDF criteria. Random-effects meta-analysis of prevalence was performed in R using logit-transformed proportions.Results Three eligible elderly-specific studies were included in the quantitative synthesis, comprising 1,444 participants. For the primary analysis, one prevalence estimate per study was retained to avoid double-counting. The pooled prevalence of MetS among older adults in Vietnam was 40.98% (95% CI: 30.29%–52.60%), with substantial heterogeneity (I² = 94.7%). In criterion-specific analyses, the pooled prevalence for NCEP-ATP III/modified NCEP-ATP III/harmonised definitions was also 40.98% (95% CI: 30.29%–52.60%), whereas the single IDF-based estimate was 22.03% (95% CI: 18.25%–26.33%). Female sex and adiposity-related measures, particularly overweight/obesity, higher body mass index, and higher body fat percentage, were the most consistently reported associated factors.Conclusions MetS appears to be highly prevalent among older adults in Vietnam, but the evidence base remains small and heterogeneous. Available data suggest lower prevalence estimates under IDF criteria than under NCEP-based or harmonised definitions. More large, standardised, community-based studies are needed to improve comparability and support public health planning.