Vitamin K is classified into phylloquinone (PK) synthesized by plants, and menaquinones (MKs) found in fermented foods. In this study, we analyzed the antioxidative and anti-inflammatory activities of PK and MKs extracted from six Sargassum species (S. horneri (Sh), S. siliquastrum (Ss), S. fulvellum (Sf), S. yezoense (Sy), S. confusum (Sc), and S. thunbergia (St); Sargassum_cVitK) and Sargassum species fermented with Lactococcus lactis (Ll; KCCM12759P) and Leuconostoc mesenteroides (Lm; KCCM12756P; ShLlLm, SsLlLm, SfLlLm, SyLlLm, ScLlLm, and StLlLm; Sargassum_LlLm_cVitK). Sargassum_cVitK contained PK and MK4 in a range of between 821.4 and 1,427.13 ng/g, with Sf (1,427.13 ng/g) and Sy (1,405.98 ng/g) showing the highest levels. Sargassum_LlLm_cVitK ranged between 666.83 and 1,403.7 ng/g, with SyLlLm (1,403.7 ng/g) and SfLlLm (1,399.69 ng/g) showing the highest levels. All Sargassum_LlLm_cVitK contained PK, MK4, and MK7; however, MK9 was exclusively observed in SfLlLm. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay showed that activities of Sargassum_LlLm_cVitK, including PK, MK4, MK7, and MK9, were slightly higher than those of Sargassum_cVitK (PK, MK4) and SyLlLm_cVitK exhibited the highest activity at 73.94%. In Raw 264.7 cells induced by lipopolysaccharide, nitric oxide (NO) production was reduced by Sargassum and Sargassum_LlLm_cVitK, indicating the anti-inflammatory efficacy of Sargassum-derived cVitK. Particularly, StLlLm and SfLlLm_cVitKs exhibited the most effective NO-scavenging activities. In conclusion, the bioconversion of Sargassum spp., including PK, and Ll and Lm producing MKs, yielded long-chain MK variants, such as MK7 or MK9. All Sargassum-derived cVitKs exhibited antioxidative and anti-inflammatory activities. These findings provide a valuable reference for future studies on the production and health-promoting effects of vitamin K.