Objective To explore histological origin and effects of the embolism during uncemented total hip arthroplasty(THA). Methods Thirty patients with ASA grade I-Ⅲ undergoing uncemented total hip arthroplasty under general anesthesia received intraoperative TEE monitoring. The incidence of embolism were observed at various operative stages (beginning of the operation, reaming of the acetabula, insertion of the acetabular prosthesis, reaming of the femur, insertion of the femoral prosthesis, relocation of the hip. Blood from right atria was sampled by central venous catheter each time for histological examination when echogenic speckles were detected. Haemodynamic and blood-gas variables were also measured repeatedly during the operative procedure.. Results Ultrasonic image of microembolus were detected in the hearts of all 30 patients, respectively 0,5,19,30,23,24 cases at beginning of operation, acetabular reaming, insertion of the acetabular component, reaming of the femur, insertion of femoral prosthesis and relocation of the hip joint. The incidences differed significantly（P＜0.05）. The percentages of embolism histologically positive at different stages were 0,0,0,47,61,38% respectively. The origin of embolism included fat drops and bone debris while the ratios were significantly different at different stages（P＜0.05）. HR, SPO2, PO2, PCO2 and PETCO2 varied little throughout the operation. However, systolic blood pressure and diastolic blood pressure markedly decreased after implantation of the femur prosthesis （P＜0.05），especially at 5 min after relocation of the hip joint. Conclusions Emboli are common during uncemented THA and most frequent at the stages of implantation of the acetabular and femoral component, reaming of the femur and relocation of the hip joint. The histological origin of embolism includes fat drops and bone debris. Intraoperative emboli gives rise to haemodynamic changes.