AMicrococcusstrain occurring frequently and isolated multiple times from stones was studied for its ability to adhere to substrates and to produce exopolysaccharides or extracellular polymeric substances, one of the essential prerequisites for biofilm formation. Measurements of the biodeterioration activity of this strain in terms of (i) pH drop, (ii) organic acid production, and (iii) weight loss of marble slabs demonstrated the highly aggressive biodeteriorating potential of the strain in question.