Adipose tissue-derived stem cells (ASC) could differentiate into endothelial cells (EC) and regarded as tissue-resident endothelial progenitor cells (EPC). Fibrin provides a provisional matrix to facilitate adhesion and migration of EC. The structural property of fibrin depends on fibrinogen concentration which influenced on cell to matrix interaction. This work was conducted to elucidate the effects of structural property of fibrin on EC differentiation. The phenotypic characteristic of ASC was assessed using FACS. Four types of fibrin were made with 0.125, 0.25, 0.5 and 1% fibrinogen and polymerized with 500 mU/ml thrombin. Fibrin structure was analyzed by SEM. ASC were induced into EC differentiation by VEGF. The EC differentiation was determined by capillary network formation and EC-specific genes expression. ASC labeled with PKH were encapsulated within fibrin and implanted into nude mice to determine in vivo angiogenesis. The ASC did not express any markers against hematopoietic cells, EC, and EPC. We could rule out the contamination of EC or hematopoietic cells. Fibrin composed by lower fibrinogen concentration disclosed wide pores and structural homogeneity, but fibrin composed by higher fibrinogen concentration resulted in smaller pores and inhomogeneous structure. There was significantly inverse relationship between capillary tube length and fibrinogen concentration (p<0.01). After 1 week induction into EC differentiation, ASC gained EC-specific genes expression and Ac-LDL uptake. The expression rates of EC-specific genes were significantly higher in ASC induced on fibrin composed with 0.125 and 0.25 % fibrinogen than other types of fibrin (p<0.05). The implanted ASC formed vascular tissue and hemoglobin content was highest in fibrin composed with 0.5% fibrinogen (p<0.05). Implanted ASC was differentiated into EC and formed capillaries and arterioles. Our results supported that fibrin could be used as substratum to support EC differentiation and structural property of fibrin was significantly affected on EC differentiation of ASC in vivo and in vitro.