Background: Acute haematologic toxicity is the most common side effect of chemoradiotherapy in patients with locally advanced cervical cancer.We are aim to test the efficacy of defined active bone marrow sparing volumetric-modulated arc therapy reduces grade 3 or higher (grade 3+) acute haematologic toxicity for patients with locally advanced cervical cancer treated with chemoradiotherapy. Methods: This was a prospective, single-center, open label, randomized clinical trial that enrolled locally advanced cervical cancer.Patients were randomized to ^99mTc sulfur colloid SPECT-defined active bone marrow sparing volumetric-modulated arc therapy group (ABMS group) or control group.The control group received weekly cisplatin concurrently with volumetric-modulated arc therapy(VMAT),followed by high-dose-rate intracavitary brachytherapy. The active bone marrow sparing volumetric-modulated arc therapy group additionally received ^99mTc sulfur colloid SPECT-defined active bone marrow dose constrain. The primary endpoint was the incidence of grade 3 or higher (grade 3+) acute haematologic toxicity. Secondary objectives included acute gastrointestinal toxicity, planning Target Volume (PTV) coverage and dosimetric parameters of organs at risk(OARs). Results: A total of 148 patients with Federation of Gynaecology and Obstetrics(FIGO) stage IB-IIIB fromJanuary 2017 to April 2019 were randomized，and 146 were treated(74 in ABMS group and 74 in control group). The median follow-up was 20.0 months.The incidence of grade 3 or higher (grade 3+) acute haematologic toxicity in the ABMS group was 29.7%,significantly lower than the 48.6% incidence in the control group(p = 0.03).The incidence of grade 3+ neutropenia (ABMS group：20.3%,control group:36.5%;p = 0.04), Grade 3+ leukopenia (ABMS group：25.7%,control group:44.6%;p = 0.02) and Grade 3+ lymphopenia (ABMS group：4.1%,control group:14.9%;p = 0.04) were significantly differences between the two group.The were no differences in Grade 3+ anemia (ABMS group：1.4%,control group:5.5%;p = 0.37) and Grade 3+ acute gastrointestinal toxicity(ABMS group：1.4%,control group:1.4%;p = 1.00) between the two group.The number of patients completing five cycles of cisplatin in the ABMS group was 88.5%,,significantly higher than the 75% in the control group(p = 0.02).There were no differences in PTV coverage and dosimetric parameters of OARs between the two group. Conclusions: SPECT-defined active bone marrow sparing VMAT signifificantly reduced grade 3+ acute haematologic toxicity,and improved chemotherapy delivery compared with control group. Clinical trial information: ChiCTR-IOR-16010214.