Abstract： Objective To investigate the clinical value of the type and the steepest slope of tumor's time-intensity curve (TIC) in assessing the pathologic response of locally advanced breast cancer treated with neoadjuvant chemotherapy (NAC). Methods Thirty-six patients with pathologically confirmed locally advanced breast cancer who finished four courses of neoadjuvant chemotherapy underwent preoperative breast MRI three times during the NAC. Pathologic response was assessed according Miller-Payne grading system, grade 4 and 5 were defined as major histological response ( MHR, n = 16) group, and grade 1 to 3 as nonmajor histological response( NMHR,n = 20)group. The type and the steepest slope of tumor's TIC were compared between two groups before NAC, after the second cycle and after the fourth cycle of NAC. ROC analysis was carried out to assess the clinical value of the TIC parameters. Results After the second cycle of NAC, the steepest slope of TIC and its first change rate were different between the MHR group [ ( 1.93 ±0.88) %/s, median 35.6%] and NMHR group [(2.73 ± 1.22) %/s, median - 11.4%] (P =0.045 and 0. 01,t=1. 09,Z= -3.64). After the fourth cycle, the proportion of type Ⅰ in MHR group (62.5% ,10/16) was significantly higher than that in NMHR group (10.0%, 2/20, P = 0.01, Z=-2. 02), and the proportion of type Ⅲ in MHR group (6. 2% ,1/16)was significantly lower than that in NMHR group (60. 0% ,12/20,P =0. 01 ,Z = -1.48). The steepest slope and its second change rate were different between the MHR group [ ( 1.33 ± 0. 52) %/s, median 56. 8% ] and NMHR group [ (2. 33 ±0. 94) %/s, median 15. 8% ] ( P ＜ 0. 01, t = 1.82, Z = - 3. 58 ). After the second cycle, the area under curve of the steepest slope of TIC and its first change rate were 0. 70 ( P = 0. 04 ), 0. 80 ( P = 0. 01 ),respectively. After the fourth cycle, the area under curve of the type Ⅰ, the type Ⅰ + Ⅱ, the steepest slope and its second change were 0. 78 ( P = 0. 03 ), 0. 69 ( P = 0. 06), 0. 82 ( P = 0. 01 ), 0. 92 ( P = 0. 01 ),respectively. Conclusion The steepest slope of TIC and its first change rate could assess the NAC response after the second cycle, and the type Ⅰ, the steepest slope and its second change could assess the NAC response after the fourth cycle.