Controllable ZnSe and ZnO structures with different morphologies were synthesized by a simple hydrothermal method. The effects of hydrazine hydrate and sodium hydroxide on the final product and morphology were studied. The results showed that controlled phase transition from ZnSe to ZnO was achieved by adjusting the volume of hydrazine hydrate. The structure variety of as-synthesized product depended on the hydrazine hydrate volume and sodium hydroxide concentration, which was further confirmed by SEM and XRD. It showed that hydrazine hydrate acted a pivotal part in the restoring process of selenium. Pure ZnSe microspheres were obtained when the volume of N₂H ₄·H₂ O increased to 10 mL. While the final product completely changed into ZnO rods when the N₂H₄ ·H₂O was absent during the synthesis process. Additionally, when the concentration of NaOH was higher than 0.5 M, ZnO tended to self-assemble into flower-like ZnO structures. The corresponding reaction mechanism was discussed. The current-voltage characteristics indicated that self-assembled flower-like ZnO structures displayed excellent electrical properties, which was attributed to the special structural feature with large specific surface area and defect states formed by adjusting the sodium hydroxide concentration. This facile approach for phase transition from ZnSe to ZnO may provide an alternative way for the preparation of functional heterostructure, which demonstrates their potential applications in optoelectronic devices.