Abstract BACKGROUND: Atherosclerosis is the most important underlying cause of cardiovascular diseases (CVD) which recently has been classified as an inflammatory disorder. Accumulation of large amounts of oxidized LDL in the intima during local inflammation reaction led to increase several factors such as C -reactive protein (CRP). It has also been reported that CRP is able to bind with modified forms of LDL as well as oxidized LDL. These findings suggest possible positive or negative involvement of this protein in atherogenesis. The main objective of the present study was to assess the influence of CRP on LDL oxidation and the possible physical \changes of LDL in the presence of CRP in vitro. METHODS: In this study, the susceptibility of purified LDL to oxidation was assayed by monitoring of formation of conjugated dienes in different physiological concentrations of CRP (0 - 0.5 -2 µg/ml) using a shimadzu spectrophotometer. Electrophoresis was used to determine the electrophoretic mobility of LDL in those conditions. RESULTS: CRP significantly reduced the susceptibility of Cu++ -induced LDL oxidation through increasing the lag timeand there was positive relationship between these findings and CRP concentration (P < 0.05). CRP caused a significant reduction in the electrophotretic mobility of LDL compared to native LDL (n-LDL) (P<0.05). CONCLUSION: A considerable reduction was shown in LDL oxidation, in higher concentration of CRP, via an unknown mechanism. The electrophoretic mobility of LDL, in the oxidative condition, decreases in the presence of CRP compared to n-LDL, which can be indicative of the effect of this protein on the physical and chemical properties of LDL. It seems that, other pathway than LDL oxidation is responsible for the effect of CRP on the atherogenesis processes. Keywords: Atherosclerosis, Creactive protein, Low-density lipoprotein, Inflammation.