we consider the generation of conductive heat trees at micro and nano scales for electronics cooling. Science and technology is racing toward smaller scales. The development of nano technology and the production of small scale electronics in recent years, the necessity of designing workable cooling systems for them will be revealed more than any other time.Due to their small scales, it is not possible to use convective paths for cooling them.Using constructal method, the tree-shape conductive paths are generated for cooling heat generating volumes. Furthermore, every feature of the tree architectures is optimized numerically to make a comparison between numerical and analytical results. Since there are some constructal tree architectures which are not possible to be generated analytically, numerical approach is used for optimization.when the smallest features of the internal structure are so small, the conventional description of conduction breaks down. hence the effective thermal conductivity exhibits the “size effect,” and is governed by the smallest structural dimension which is comparable with the mean free path of the energy carriers. Therefore we consider models which were proposed for small scale bodies. As mentioned above, in this thesis, analytical and numerical approaches for generating heat trees are considered. Finally tree shape structures including radial, branching, loop architectures are generated. The performance of these structures based on different geometrical features is compared.It is apparent that increase in the degrees of freedom leads to a better performance. However, considering high conductive paths with variable cross sections for cooling a disc shape body does not improve its performance, astonishingly. Moreover, in this research, we consider the generation of conductive heat trees including elemental volumes, first construct, second construct and third construct architectures for cooling a heat generating rectangular body. It is shown that minimal thermal resistance of structures with high conductivity inserts of optimally varying thickness decreases considerably in comparison with that of structures with inserts of constant thickness.It is shown thatThere exists an optimal constructal order corresponding to the minimum heat resistance. It is in accordance with what contructal theory claims that despite what fractal theory believes, increase in complexity does not always lead to a better performance. For example, in bulk region, it is shown that minimal thermal resistance increases when the order of construct becomes more than one. Moreover, it implies that although increase in the order of construct does not necessarily lead to better performance, in a specified order of construct,the increase in the degrees of freedom will definitely lead to a better performance. Keywords: conductive paths,constructal theory