Hundreds of Patients without infection (age 18 to 60 years old) developed Chronic ITP. All patients will be enrolled in this study and will be randomly assigned to receive 100 mg rituximab weekly for 4 weeks (group A) or a single dose of 375 mg/m2 rituximab (group B). After treatment all patients will be followed for two years. During observation platelet count and B lymphocyte will be detected every month.