Twenty five rabbits at Periyavadi village of Pudukkottai district of Tamil Nadu during the month of November – December, 2004 were reported to have died suddenly without showing any clinical signs except dullness, anorexia and overcrowding. Post-mortem examination of the carcasses revealed petechial haemorrhages in lung and liver and ecchymotic haemorrhages in trachea.  Escherichia coli were isolated from the liver, lung and tracheal samples and identified based on morphology, cultural characters and biochemical reaction. The antibiotic sensitivity test of E. coli revealed sensitivity to Ciprofloxacin, Chloramphenicol, Endrofloxacin and Nalidixic acid and resistance to Ampicillin, Cloxacillin and Kanamycin. Over crowding, poor feeding, poor ventilation, improper cleaning of urine and fecal materials and general mismanagement of the rabbits were observed in this study which could be of predisposing factors for the occurrence of colibacillosis. All the rabbits were shifted to a well ventilated house and sick animals were treated with Ciprofloxacin 20mg / kg body weight orally twice a day for 5 days and the rabbits responded well to antibacterial therapy.