A clean bowel preparation prior to X-ray examination is essential to obtain an accurate diagnosis. This study was performed to compare the effect of senna and castor oil on the bowel preparation of dogs for abdominal radiography. Twenty adult healthy mongrel dogs from each sex ranging in age from 18 to 30 months received either a senna (20mg/kg) or a castor oil (4ml/kg) regimen through an orogastric tube the day before abdominal radiography. Only water was given ad libitum to animals during the day before radiography. Radiologist unaware of the method of bowel preparation, reviewed the standard radiographs and graded the feces and gas in the colon and rectum, fecal radio-opacity and quality of radiographs on a scale of 0 to 3 (0=inadequate to 3=excellent). The cleanliness scores of colon for the senna and castor oil groups were 2.5±0.53 and 2.3±0.48, respectively. Also the cleanliness scores of rectum for the senna and castor oil groups were 2.5±0.53 and 2.4±0.52, respectively. Both senna and castor oil significantly improves bowel cleansing score in dogs (p < 0.05). There were no significant differences between the groups with respect to colon and rectum cleansing score, fecal radio-opacity and quality of radiographs (p ≥0.05).There were no clinically differences between the two groups for any of the side effects. It is concluded that senna and castor oil are safe and effective methods of colon cleansing, well tolerated by dogs.