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The Os nuclei lie in the beginning of the transitional region between the well deformed rare earth and spherical lead isotopes. The nuclei in this region are believed to be soft to changes in gamma deformation due to the softness of nuclear potential which may result in the shape coexistence. The neutron Fermi levels in Os nuclei from A = 170 to A = 186 lie in the middle of i13/2 orbital so that their shape in the ground state tends to take an appreciable prolate deformation. Hence collective bands with the well defined moment of inertia occur and the effect of different proton orbitals is observed as a modulation of the prolate structure. The anomalies in the yrast sequence, an effect attributed to change in moment of inertia of the ground state rotational band and the band crossing phenomena, are very important and vary strongly with neutron number in case of Os nuclei. The nuclear structure of 178Os nucleus has been studied using the reaction 165Ho (20Ne, p6n) 178Os. Indian National Gamma Array (INGA) consisting of six Clover detectors with anti Compton shields was used for the detection of resulting gamma rays. The Direction Correlation of γ-rays de-exciting Oriented states (DCO) ratio and polarization of gamma rays were measured to assign spin, parity and multipolarity of transitions. Twenty one new transitions belonging to the 178Os nucleus have been identified. The sudden and rather strong gain in aligned angular momentum is observed in the yrast band of 178Os. A new aligned rotational band similar to 180Os is also discovered in this nucleus. This band exhibits a very complex decay pattern with a single linking transition of 1778 keV to the ground state band. The tri-axial shape co-existence is also observed in this nucleus at higher excitation. The experimental results are compared with the Microscopic Hartree-Fock model calculations. [ABSTRACT FROM AUTHOR]