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Two novel marine actinobacteria, designated as SCSIO 60955 T and SCSIO 61214 T , were isolated from deep-sea sediment samples collected from the South China Sea. The cells of these organisms stained Gram-negative and were rod shaped. These strains were aerobic, and catalase- and oxidase-positive. Optimal growth occurred at 28 °C and pH 7 over 14 days of cultivation. Both strains possessed phospholipids and phosphoglycolipids. The main menaquinone was MK-7. The major fatty acid was C 16:0 . The peptidoglycan structure was type A1γ' (meso-Dpm). Analysis of genome sequences revealed that the genome size of SCSIO 60955 T was 3.37 Mbp with G + C content of 76.1%, while the genome size of SCSIO 61214 T was 3.67 Mbp with a G + C content of 74.8%. The ANI and 16S rRNA gene analysis results showed that the pairwise similarities between the two strains were 73.4% and 97.7% and that with other recognized Thermoleophilia species were less than 69.1% and 87.8%, respectively. Phylogenetic analysis of the 16S rRNA gene sequences showed that strains SCSIO 60955 T and SCSIO 61214 T were separately clustered together and formed a well-separated phylogenetic branch distinct from their most related neighbor Gaiella occulta. Based on the data presented here, these two strains are proposed to represent two novel species of a novel genus, for which the name Miltoncostaea marina gen. nov., sp. nov., with the type strain SCSIO 60955 T (=DSM 110281 T =CGMCC 1.18757 T ), and Miltoncostaea oceani sp. nov., with the type strain SCSIO 61214 T (=KCTC 49527 T =CGMCC 1.18758 T ) are proposed. We also propose that these organisms represent a novel family named Miltoncostaeaceae fam. nov. of a novel order Miltoncostaeales ord. nov., (Copyright © 2021 Elsevier GmbH. All rights reserved.)