Background:Antiphospholipid antibodies are a heterogeneous circulating immunoglobulins family of approximately twenty auto antibodies directed against phospholipids binding plasma proteins. Anticardiolipin (ACL) is the most commonly investigated APL in relation with several diseases as Rheumatoid arthritis, systemic thrombosis, cerebral ischemia, deep vein thrombosis. Anti-cardiolipin antibodies can be classified in two ways; As IgM, IgG or IgA and As ß2-glycoprotein dependent or independent. Rheumatoid arthritis is a systemic autoimmune disease that presents as a symmetrical inflammatory polyarthritis which affects the smaller joints such as hands and feet first, before affecting larger joints and there are six main types of arthritis. Objective: This study aimed to investigate the Seroprevlance of ACL among Rheumatoid arthritis patients. Materials and Methods: This is a case-control study conducted in an Integrated Mdedical Lab and Al-borg Medical Laboratories in Khartoum, sudan, from September to November 2016. It included ninety subjects; 60 of them were cases and 30 were control subjects, Physical examination, IgG and IgM anti-cardiolipin assay investigated using in vitro ELISA and WBCs, PLT, Hb, HCT and RBCs using Sysmex ® Kx21-N hematology analyzer were done for each subject. Results: Mean age among control was (42±18) and (42±14) among cases.Hb, HCT RBCs, WBCs and PLT were within the normal range but among control were higher than cases with significant association except WBCs; p= (0.000), (0,000), (0.000), (0.056), (0.002) respectively. The majority IgG and IgM were seronegative with significant association p= (0.015) and (0.005) respectively. Finally, a significant correlation was appeared between age and Hb, WBCs and PLT at 0.05 level (r= 0.329*,p=0.010), (r= 0.270*, p= 0.037), (r= -0.258* p= 0.047) respectively and Hb with both WBCs and RBCs; (r= 0.286*, p=0.027), a weak negative relationship between TWBCs and PLT at 0.01 level (r= 0.403** , p= 0.001). Conclusion: This study concluded that there was a strong effects of rheumatoid arthritis activity on both ACA and WBCs, PLT, Hb, HCT and RBCs normal ranges.