This prospective study was done for to see the efficacy of preoperative use of granisetron plus dexamethasone (Group A) & granisetron (Group B) alone for the postoperative prevention of nausea & vomiting after tonsillectomy operation. One hundred patients undergoing tonsillectomy & adenoidectomy operation under general anaesthesia who were admitted in the Mymensingh Medical College Hospital during the period from July 2008 to June 2009 with American Society of Anaesthesiologists (ASA) grade I & II with age 3-40 years, body weight 10-60 kgs, were studied. Observation of this study was analyzed in the light of comparison between the two groups. All results were expressed as mean±SEM. Age in Group A 15.98±1.028 & Group B 17.18±0.961 years; Weight in Group A 38.40±1.492 & Group B 39.76±1.561 kgs and operational duration in Group A 52.60±0.786 & Group B 52.70±0.823 minutes. The studied groups were statistically matched for age, weight, duration of surgery. We observed that the effects of combination of granisetron & dexamthasone are more than granisetron alone in prevention of nausea & vomiting after tonsillectomy operation. The frequency of vomiting was 4% in combination & 16% in single therapy which is statically significant (p<0.05).