A characteristic toxicity of niraparib is a decrease in blood platelets (PLT), with an incidence of ~ 34% for grades 3 - 4 conditions. However, exceedingly severe cases have been reported infrequently. This paper describes three patients with acute and refractory severe PLT deficiency due to niraparib administration. The symptom characteristics, treatment course, and outcomes have also been analyzed, and the potential for the involvement of immune-related factors is considered. Therefore, it is recommended to comprehensively assess bone marrow hematopoietic function and high-risk variables before administering niraparib, intensify self-management and monitoring of patients, track changes in indicators, and intervene promptly. Additionally, if standard PLT-elevating therapies are ineffective, early full-dose administration of thrombopoietin receptor agonists, preferably avatrombopag, may be beneficial for reversing PLT loss of control.