Abstract: To prepare a selenium-enriched probiotic fermented milk, Lacticaseibacillus paracasei SCFF20, a selenium-enriching strain isolated in our laboratory, was employed to ferment milk at 42 ℃ for 12 hours. The physicochemical indexes, selenium content, flavor compounds and some other indicators of the prepared fermented milk were systematically evaluated. Four experimental treatments were conducted as follows: SF group was performed using commercially available L. paracasei. BF group was performed using L. paracasei SCFF20 alone. XF group was performed using L. paracasei SCFF20 and selenium nanoparticles (SeNPs), and YF group was performed using L. paracasei SCFF20 and sodium selenite. Results showed that the XF group exhibited significantly higher Se(0) content (4.05±0.01 mg) and a^* value (1.30±0.02) compared to other groups (P<0.05), demonstrating L. paracasei SCFF20’s ability in selenium biotransformation and its synergistic effect with SeNPs during milk fermentation. Furthermore, electronic nose and GC-MS analysis indicated that both L. paracasei SCFF20 and commercial L. paracasei contributed esters, alcohols and aldehydes to the flavor profile of the fermented milk. Notably, the XF group showed enhanced flavor diversity, particularly in esters (e.g., ethyl palmitate) and acids (e.g., 2,3-dihydroxypropionic acid) compared to the SF group. Therefore, the incorporation of L. paracasei SCFF20 with SeNPs markedly improved both the selenium content and flavor complexity in the fermented milk. This study provides a theoretical basis for research on biogenic selenium-enriched fermented milk and its related product development.