In this study, orange flavored soft drink samples sweetened with 100% aspartame (0.5 g/L) were stored in three different pH values and temperatures. The samples with the pH values of 2.75, 3.25, and 4.57 were kept in 20, 30, and 40 degrees C temperatures over a period of 5 months. The remaining aspartame was determined at the 1st, 2nd, 3rd, 4th, and 5th months by HPLC. In the same pH groups, it was clearly observed that stability of aspartame decreased with increasing storage temperature. It was also determined in each of the same pH groups that aspartame stability increased as the pH value was raised from 2.75 to 4.57. Aspartame was the least stable at pH 2.75 when stored in 40 degrees C, whereas it was the most stable at pH 4.57 and 20 degrees C. At the end of 5th month in 40 degrees C, stability tests could not be performed and remaining aspartame could not be determined.