Four new chlorinated carbazole alkaloids, chlocarbazomycins (CCBs) A—D, were isolated from sponge associated bacterium Streptomyces diacarni LHW51701. Their structures were elucidated via spectroscopic techniques (including HRESIMS, 1D & 2D NMR), and X-ray crystallographic analysis. Structurally, the 4-chloro coupled with 3-methoxyl substituents in the tricycle nucleus of CCBs A—D and the N-methoxyl group of CCB-D are rare in naturally occurred tricyclic carbazole alkaloids. Moreover, CCBs A—D do not bear the typical C1 para-alkyl and C2 meta-methyl side chains of bacterial tricycle carbazoles, suggesting a novel mechanism of aromatic ring formation in biosynthesis. The biological evaluation showed that CCB-C possessed inhibitory activities against pathogenic microorganisms including methicillin-resistant Staphylococcus aureus (MRSA), Mycobacterium smegmatis, Bacillus mycoides, and Candida albicans. © 2021 SIOC, CAS, Shanghai and Wiley-VCH GmbH