The first calcium complex from nature, Coumamarin (1), 7-hydroxy-3-methoxy-2-oxo-2H-chromene-6-carboxylate Ca(II) complex, was isolated from Aspergillus sydowii ASTI, together with diorcinol (2), violaceol I (3), hydroxysydonic acid (4), cyclo (Trp-Phe), kojic acid, ergosterol, and uracil. The producing strain was isolated from marine water sample collected from Tiran Island, Red Sea, Egypt. Structure 1 was assigned by intensive 1D, 2D NMR, HR-ESIMS, and X-ray crystallography as well. Coumamarin is potentially active against certain tested bacteria and yeasts, while showing no cytotoxic activity against human cervix carcinoma cell line (KB-3-1). Taxonomically, the fungus was identified by phylogenetic analysis of its 18S rRNA gene sequence.