Abstract: This study investigated Lactiplantibacillus plantarum NM18 isolated from fermented mare's milk in Inner Mongolia and its extracellular polysaccharide (EPS-5), with examinations conducted on EPS-5's particle size and zeta potential, thermodynamic properties, emulsifying properties, and antioxidant activity. The whole genome of strain NM18 was sequenced for the identification of functional genes. In particle size and zeta potential experiments, the smallest particle size (an average diameter of 338 nm) and the highest uniformity were exhibited by a 1 mg/mL EPS-5 solution, while the greatest stability (a zeta potential of −20.87 mV) was demonstrated by a 0.25 mg/mL EPS-5 solution. Good thermal stability across the temperature range of 30 ℃ to 238.2 ℃ was exhibited by EPS-5. Furthermore, good emulsifying ability for several common vegetable oils was demonstrated by EPS-5, with the order of emulsifying strength being: peanut oil>rapeseed oil>sunflower seed oil>soybean oil. The emulsion stability of these vegetable oils was effectively maintained by a 2 mg/mL EPS-5 solution. Furthermore, scavenging activity against DPPH radicals, hydroxyl radicals, and hydrogen peroxide was exhibited by EPS-5. The complete genome sequence of strain NM18 spanned 3419686 bp with an average GC content of 44.3%, comprising one chromosome and six plasmids. A total of 3255 protein-coding sequences (CDSs) were contained in the entire genome, with 78.59% of CDSs assigned to COG categories. Carbohydrate genes were grouped into four major categories, and four secondary metabolite gene clusters (RiPP-like, T3PKS, terpene, and cyclic-lacto), along with 18 genes associated with the biosynthesis, regulation, secretion, and transport of extracellular polysaccharides (EPS) produced by strain NM18, were identified. A complete EPS synthesis gene cluster was also identified. A theoretical foundation for the development and utilization of strain NM18 is established by these findings, and experimental evidence for studying the functional characteristics of EPS-5 and for product development is also provided.