Non pharmacologic approaches to overcome post operative nausea and vomiting include giving pre-operative hydration. The objective of this study was to learn the efficacy of pre-operative lactated Ringer’s solution (2 mL/kgBW/hour) in fasting patients to overcome the post-operative nausea and vomiting in mastectomy surgery. This study was a randomized clinical trial that conducted in March to April 2013 in Dharmais Hospital-National Cancer Center, Persahabatan Hospital, Fatmawati Hospital, and Rumah Sakit Cipto Mangunkusumo Jakarta to patients with American Society of Anesthesiologist (ASA) physical status 1–2. A total of 102 patients were randomized into the hydration group and control group. Data analysis was performed using chi-square test or appropriate test using SPSS ver. 15. There were statistically significant differences in the incidence of nausea at 0–1 hour post-operative (19.6% in hydration group vs. 39.2% in control group) and at 0–24 hours post-operative (21.6% in hydration group vs. 41.2% control group). The incidence of 1–24 hours PONV, although not statistically significant, was higher in the control group (11.8% in hydration group vs. 23.5% in control group). There was no difference in vomiting incidence between the two groups. Pre-operative lactated Ringer’s solution 2 mL/kgBW/hour in fasting patients effectively reduces the incidence of post-operative nausea one hour after operation.