Pyothorax associated with a Mycoplasma sp and Arcanobacterium pyogenes was diagnosed at necropsy in a 1-month-old female Van kitten. The pleural cavity contained approximately 50 mL of blood-tinged, reddish-brown, nonodourous fluid bilaterally. Gram positive coccobacilli were seen in the exudate from necrotic plaques on the pleurae. Mycoplasma sp and A pyogenes were isolated from a sample of the fluid in the pleural cavity. The concomitant presence of Mycoplasma sp and A pyogenes could be considered another variation on the polymicrobial nature of pyothorax and associated pleural lesions in cats.