Phenazine derivatives, a class of naturally occurring antibiotics primarily produced by bacteria, are regarded as promising scaffolds for developing new antibiotics. In this study, eight new dimeric phenazine derivatives, phenazostains K‒R (1‒8), along with two reported dimeric analogues, phenazostains B (9) and C (10), were isolated from the fermentation broth of the marine-derived Streptomyces sp. OUCMDZ-4923. Their structures were elucidated through spectroscopic analysis, primarily using NMR and HRESIMS spectra, ECD calculations, and the modified Mosher's method. Compounds 1‒10 feature the 12-deoxysaphenate unit linked to various sites on methyl saphenate, phenazine, or methyl phenazine-1-carboxylate. Notably, compounds 1 and 2 represent the first dimeric phenazines linked by a 12, 12'-oxy bridge. Our experimental results suggest that these dimers could be formed from methyl saphenate (12) through a nonenzymatic pathway. Moreover, the analysis of gene roles within their biosynthetic gene cluster revealed that phenazostains 1‒8 are formed through a nonenzymatic process. Additionally, all dimers were evaluated for their antibacterial activity; compounds 1, 3‒5, and 9 exhibited inhibitory activities against both Staphylococcus aureus and its methicillin-resistant strain (MRSA), with MIC values ranging from 1.56 to 25.0 μg/mL.