Dilatation is the most significant complication of prosthetic vascular grafts. It is suspected to be a nidus of other graft complications. There have been a few studies on in-vitro-dilatation of the prosthetic vascular grafts. This is due to the lack of an effective and simple method to measure the transverse dilatation of the graft. We developed a new simple, reliable and cost-effective technique to evaluate the in-vitro-dilatation of prosthetic vascular grafts. The dilatation behavior of two different types of grafts (dacron and PTFE) was observed and compared under static pressure between 0 and 300 mmHg. The in-vitro- dilatations of dacron and PTFE grafts were 6.9% and 8.4% respectively. Interestingly, the dilatation rate for PTFE vascular grafts is higher than the indicated rate in the literature.