The study aimed to evaluate the retention and fracture resistance of composite core to differently designed dowel heads. To conduct this study, forty samples were prepared. Samples were divided into four groups (n=10) according to post head design, each group was further subdivided into two subgroups (n=5) according to the type of test used. Sub group A: samples were subjected to push out test. Subgroup B: samples were subjected to fracture resistance test. Push Out Test: For push out test (subgroup A) twenty samples were prepared, five for each group. Two special designed copper pipes were fabricated to act as core formers. MultiCore Flow (dual cured composite resin) was used as core material; core length was standardized to 6mm which is the length of the longest post head used in this study. Fabricated cores were subjected to an apico-coronal force till failure occurred. Control group (smooth surface post) showed the lowest mean push out bond values, because smooth surface posts depend only on chemical bond between the post and core. The other groups showed statically higher bond strength, due to the presence of mechanical interlocking between the fiber post and cores. Fracture resistance test: For fracture resistance test (subgroup B) twenty samples were prepared, five for each group. Freshly extracted teeth were endodontically treated. Mechanical instrumentation was done using Protaper hand files, to standardize canal size. Canals were obturated using Protaper gutta-percha and ADSEAL resin based sealer was used. Ferrule preparation was done using tapered with flat end stone to produce shoulder finish line. Decoronation using diamond disc 2mm above the mid proximal cementoenamel junction was done. Enlargement of canals was done using Pesso-reamer, followed by the drill supplied by the manufacture. Post cementation and core built- up was done using MultiCore Flow (dual cured composite resin). Teeth were subjected to loading by an angel of 135º to the long axis of the tooth till failure occurred. Group 2 (Parapost) showed the lowest mean fracture resistance in comparison to other groups, this may be due to lower fiber content in comparison to other groups in this study. Within the conditions used in this study, the following conclusions may be drawn: 1-Post head designs affect greatly post and core bond strength. 2- Triple conical frustum (Fibrekleer) post is considered the most appropriate choice for optimum post and core bond strength. 3- Arrowhead post (Achromat) is considered as the second choice for post and core bond strength. 4- Smooth surface post (Glassix) affected negatively the bond strength 5- High fracture resistance of post and core complex depend on the geometry of the post head, amount and orientation of fibers. Clinical recommendation: 1- It is recommended to use fiber posts having high fiber content. 2- Fiber posts with undercuts in their heads increase the surface area of the bonded surface and thus allowing mechanical interlocking. 3- It is not recommended to use posts having sharp edges or angles, as they will cause stress concentration within the core, leading to micro-cracks and failure.