Thioquinomycins A-D (1-4), four novel naphthothiophenediones were isolated from the rice-based medium of the marine-derived Streptomyces sp. SS17F. Their structures were elucidated by spectroscopic methods and HRESIMS data. The absolute configurations of all the compounds were elucidated by X-ray diffraction analysis, ECD and Mosher's method combined with 19F-NMR. Compounds 1-4 showed moderate cytotoxicity against NCI-H1975 with IC50 values from 17.5 to 50 µM. In addition, compounds 1-4 also exhibited inhibitory activities against PKCα and ROCK2 protein kinase.