The objective of study was to evaluate the clinical values of multiparameter flow cytometry (MPFC) and cytomorphology of bone marrow aspiration(BMA) in detecting bone marrow involvement in patients with B cell Non-Hodgkin's lymphoma (B-NHL). 96 bone marrow samples from the patients with B-NHL were measured by MPFC using CD45/SSC and CD20/SSC gating strategy combined with anti-kappa and anti-lamda monoclonal antibodies, and then compared with results acquired by cytomorphologic analysis of BMA. The results showed that the bone marrow involvement was confirmed by MPFC in 38 cases (39.6%), while it was detected by cytomorphologic analysis of BMA only in 12 cases (12.5%). There was a significant difference between the two methods (p<0.05). 12 positive cases detected by cytomorphologic analysis of BMA were also positive by MPFC. There was no difference of 3-year overall survival rate between negative and positive cases detected by MPFC, but their 4-year overall survival rate was 73.18+/-6.65% and 44.13%+/-19.55% respectively (p<0.05). It is concluded that the MPFC is a more sensitive method for detecting bone marrow involvement in patients with B-NHL than cytomorphologic analysis of BMA. The 4-year overall survival rate of the patients without bone marrow involvement was significant higher than those of patients with bone marrow involvement. Bone marrow involvement in B-NHL detected by MPFC can be useful for clinical evaluation and prognosis prediction.