This study aimed to determine the effect of aspartame on the dopamine concentration in brain adult rats. For this study 24 adult male rats and 24 adult female rats were used, with age of 60-65 day, and an average live weight between (165-185) gm. The experiment has designed depend on the concentration on the daily dose, where the animals randomly divided into three groups, each group contains 12 animals (six males & six females). And the control group included six males and six females as well. The first group G A gavagedwith aspartameconcentration of (40 mg / kg/ per day), the second group G B gavage with concentrated aspartame (54 mg/kg/per day) and the third group G C gavage aspartame dosed of (70 mg/ kg/ per day), while the control group dosed with 1ml physiologic solution daily. All groups had their daily dosages through the mouth, and the experiment continued from October 2015- January 2016. After the dosage’s period of time completed, samples of blood were taken to study the concentration of the dopamine in the brain.The results of the study showed that; rats not have significant differences (P> 0.05) in dopamine concentration in animals’ brain from the first group G A comparing with control group. The second group G B, which dosed with concentration dose (54 mg/ kg/ per day), did not show significant differences (P >0.05) when it compared with control group for both sexes. As well the third group dosed with concentration dose (70 mg/ kg/ per day), showed highly significant decrease (P <0.01) in the level of dopamine in the brain comparing with control group and other groups . conclude from study that the high concentration of aspartame lead to decrease the dopamine concentration in brain rats, also conclude that female rats were more sensitive to aspartame than male .