Objective To systematically evaluate the correlation between serum 25-hydroxyvitamin D [25(OH)D] level and mortality risk in adult with sepsis. Methods We searched PubMed, Cochrane Library, Embase, China National Knowledge Infrastructure, Wanfang, and Chongqing VIP databases for studies on the correlation between serum 25(OH)D and mortality risk in adults with sepsis. The search period was from the establishment of databases to December 2023. Meta-analysis was conducted using RevMan 5.4 software. Results A total of 9 studies were included, with a total of 2267 patients. The meta-analysis results showed that sepsis patients with low serum 25(OH)D levels (<30 ng/mL), insufficient levels (20-30 ng/mL), and deficient levels (<20 ng/mL) had a higher mortality risk compared to those with normal levels (relative risk=1.96, 1.62, 2.21, P<0.05). Subgroup analysis based on different sepsis diagnostic criteria, regions, and research types also showed that sepsis patients with lower serum 25(OH)D levels (<30 ng/mL) had a higher mortality risk compared to those with normal levels (P<0.05). Conclusions Adult sepsis patients with low serum 25(OH)D levels have a higher mortality risk than those with normal levels.