Objective: To compare castor oil and sodium phosphate preparation (Swiff) in patients' satisfaction, efficacy for colon cleanness, side effects, and prices. Material and Method: One hundred patients referred for barium enema were randomized to receive castor oil (n = 50) and sodium phosphate preparation (n = 50). They graded their satisfaction using a 5-point scale (easy, acceptable, slightly difficult, extremely difficult, and unacceptable). The efficacy for colon cleanness was graded by two radiologists using a 5-point scale (excellent, easy for evaluation, acceptable, difficult for evaluation, and unacceptable). Side effects were evaluated by patients' vital signs, total number of bowel frequency, and 10 associated symptoms. Results: Both preparations revealed no difference in patients' satisfaction (p = 0.882) and efficacy of colon cleanness (p = 0.130). Sodium phosphate preparation was more expensive (79 vs. 10 Baht) and caused higher number of bowel frequency (p < 0.001). Conclusion: With a cheaper price, castor oil was comparable with sodium phosphate preparation in patients' satisfaction and efficacy of colon cleanness.