In the present study, out of 200, 120 (60%) Plectropomus maculates fish were found to be naturally infected with Kudoa sp. The infection was intensive and appeared as clusters of ovoid to ellipsoidal plasmodia being restricted to the cardiac muscles. More than 100 plasmodia were counted per infected heart and measured 1.53 ± 0.2 (1.2-2.5) × 0.65 ± 0.2 (0.63-0.80) mm. On the basis of spore morphology, the parasite was identified as Kudoa sp. The spore measures 4.8 ± 0.3 (4.7-6.8) × .0 ± 0.3 (4.6-6.5) μm. The four polar capsules were pyrifom in shape measuring 1.4 ± 0.2 (1.3-3.5) × 1.2 ± 0.2 (1.1-2.2) μm. Transmission electron microscopy showed that the plasmodia were bordered by a single membrane which invaginates into pinocytotic canals. Adjacent to the plasmodial wall, the generative cells and the early pansporoblasts were located peripherally. The developmental stages characterizing sporogenesis, capsulogenisis, and valvogenesis of the present parasites were ultrastructurally studied.