BACKGROUND Spinal manipulation, particularly in cervical rotatory manipulation (CRM), has become increasingly popular in physical therapies, with satisfying effect. However, it is still unclear whether CRM affects internal carotid arteries (ICA) with mild carotid atherosclerosis (CAS), especially in hemodynamics. MATERIAL AND METHODS Nine cynomolgus monkeys were randomly divided into 3 groups: the CAS-CRM, the CAS, and the blank control groups. CAS models were developed in the left ICA in the CAS-CRM and the CAS groups. The monkeys in the CAS-CRM group underwent CRM intervention for 3 weeks. Histology and hemodynamics were measured, including peak systolic velocity (PSV), end-diastolic velocity (EDV), time average velocity (TAV), resistance index (RI), and pulsatility index (PI). Measurements were made separately at 3 different rotation angles (0°, 45°, and 90°). RESULTS In the 3 groups, with the increase of rotation angle, the decreasing tendency of PSV, EDV, and TAV and the increasing tendency of RI and PI were statistically significant. At each angle, the monkeys in the CAS-CRM and the CAS groups had lower levels of PSV, EDV, and TAV and higher levels of RI and PI compared with the blank control group. No significant difference in hemodynamics was found between the CAS-CRM and the CAS groups. CONCLUSIONS Both the rotational angle and the atherosclerotic disease can affect the blood flow of the ICA. However, CRM does not cause adverse effects on hemodynamics in cynomolgus monkeys with mild CAS, and appears to be a relatively safe technique.