Some studies have demonstrated that chemotherapy drugs enhance sensitivity to anesthetics owing to its systemic toxicity, while others have demonstrated that chemotherapy drugs have no effect. This study aimed to determine whether neoadjuvant chemotherapy influences the effect-site concentration (Ce) of propofol for sedation in patients withbreast cancer.Methods: This study included patients aged 19–75 years who were scheduled to undergobreast cancer surgery under general anesthesia. Patients who received neoadjuvant chemotherapy were assigned to group C, whereas those who never received chemotherapy wereassigned to group N. Propofol was administered through an effect-site target-controlled infusion, and the Modified Observer’s Assessment of Alertness/Sedation scale (MOAA/S) scoreand Bispectral Index (BIS) were recorded. When the plasma concentration and Ce wereequal to the target Ce, and if the MOAA/S score did not change, the target Ce was increasedby 0.2 μg/ml; otherwise, the Ce was maintained for 2 min and then increased. This processwas repeated until the MOAA/S score became 0.Results: No significant differences were observed in Ce values at each sedation level between both groups. Ce values for loss of consciousness (LOC) of groups C and N were 2.76± 0.29 and 2.67 ± 0.27 μg/ml (P = 0.285), respectively. However, the BIS value at LOC ofgroup C (63.87 ± 7.04) was lower than that (68.44 ± 6.01) of group N (P = 0.018).Conclusions: Neoadjuvant chemotherapy for breast cancer has no effect on the Ce ofpropofol for sedation.