Background of Study: Sickle cell anaemia (SCA) is a common monogenetic disorder that is characterized by chronic haemolysis, recurrent vaso-occlusion of the microcirculation and chronic inflammation. Nitric oxide (NO) bioavailability has been found to be impaired in sickle cell disease this is because haemoglobin released during intravascular haemolysis, is a potent scavenger of nitric oxide (NO) and also releases arginase into the plasma. Upon release, arginase metabolizes plasma L-arginine into ornithine, reducing the needed substrate for nitric oxide synthesis and compounding the reduction in nitric oxide bioavailability in SCA. Objective: The aim of this study was to determine the plasma level of L-arginine in adult patients with SCA in steady state and compare with those of age and sex matched normal HbA controls. Methods and Materials: Thirty adult SCA patients in steady state attending Haematology clinic at University College Hospital, Ibadan, Nigeria and 30 normal HbA age and sex matched controls were enrolled for this study. Haematological parameters were determined by a 5-part autoanalyzer and plasma level of L-arginine was quantified by ELISA method. Data were analyzed and results were considered statistically significant if p<0.05. Result: The respondents consist of 33(55) females and 27(45%) males with a mean age of 29.4years (8.9). Haematocrit was significantly higher in controls than steady state, Plasma L-arginine was significantly reduced in SCA patients in steady state than controls. Conclusion: This study confirmed that there is reduction in L-arginine in SCA patients in steady state compared to normal HbA controls.