Objective: This study evaluated the microleakage of endodontically treated teeth restored with fiber posts cemented with two different adhesive protocols under thermodynamic loading.Materials and methods: Twenty intact human lower premolars were de-coronated 1mm above the (CEJ) and endodontically treated and prepared to receive glass fiber posts using special drill supplied with post manufacturers. The samples were divided into two main groups, G1: fiber posts (n=10) were cemented with a Total etch adhesive resin cement (RelyX ARC Cement). G2: fiber posts (n=10) were cemented with self-Adhesive resin cement (RelyXUnicem Cement). Then, each group was furthermore subdivided into two sub-groups of five teeth for each group (control group (nTDL); the samples were not subjected to thermodynamic loading. and tested group (TDL): each samples was subjected to cyclic loading 100000 impacts 2cycle per second at an angle 45ο to the long axis of the tooth followed by thermalcycling of 2000 cycles between 55cο and 5cο at a dowel time of 10second.Results: revealed that the self- Adhesive resin cement showed highermicroleakage than the Total etch adhesive resin cement in all groups with no significant difference .for tooth segments the highest microleakage was seen in the coronal sections than other sections with highly statistically significant difference (P=0.0001).Conclusion: Microleakage of the cemented fiber posts was slightly varied with the type of luting agents, artificial aging and highly varied in different region inside the root canals.