Adhesion of leukocytes endothelial cells of arteries and their migration into the vessel wall is the critical event in initiation of atherosclerosis. This process is caused by the up regulation of adhesion molecules on endothelial cells and an increased expression of chemotactic factors to monocytes, in the vascular wall. Gene silencing by small interfering RNA (siRNA) has emerged as a useful technology for assessment of gene function and study of gene-gene interactions. The active agent, short interfering RNA (siRNA), are known to vary in silencing capacity depending on the position in the mRNA target. The validation of designed siRNA molecules as to their silencing efficiency is carried out in vitro cell based assay. In present study U937 cell line is used as a model as they are differentiating monocytes that express VCAM-11. The designing of perfect siRNA is a crucial step and involves the use of various bioinformatics tools. Presents study aimed at designing and in vitro validation of human VCAM-1 siRNA by qPCR and assessment of their immunotoxicity effect in U937 cells.