Abstract: Objective To explore ultra-structural changes of fat embolism syndrome（FES） in the lung. Methods Fat embolism animal model was developed by fat intravascular injection to the experimental rabbits. The rabbits were sacrificed after thrombosis immediately（0 h）, 3 h, 8 h and 1 d, 2 d, 7 d, 14 d after thrombosis, respectively. Rabbits were injected with the same dose of saline in the control group. All experimental procedures were same in experimental and control groups. The animal model of fat embolism was validated using HE and Sudan Ⅲ staining. Ultra-structural changes of lung were observed by using transmission electron microscopy. Results Ultra-structural changes in capillaries and small blood vessels were found in experimental group. Type Ⅱ alveolar cells, related cells and organelles showed time-dependent changes. Lipid drops and inflammatory cells were not found in control group. Lamellar body did not show emptying phenomenon and the amount of lamellar body was normal. Conclusion The study could provide the theoretical principle for fat embolism cases in forensic pathology.

Key words: forensic pathology, embolism, fat, rabbits