The broad applications of titanium dioxide (TiO2) in various fields have drawn attention for the synthesis of TiO2 nanoparticles. In line with this requirement, there are various studies on the synthesis of TiO2 nanoparticles. Many chemical and physical methods have been applied to prepare nanoparticles, but synthesis methods utilizing biological materials (e.g., bacteria, fungi, enzymes, and plant extracts) can be considered as eco-friendly alternatives when compared to chemical and physical techniques. The present study was designated to biotechnologically synthesize TiO2 nanoparticles from titanium(IV) oxide by Aspergillus sp. TK4. TiO2 nanoparticles were successfully synthesized extracellularly from the precursor and characterized by using SEM and EDX techniques. According to the results of SEM and EDX, the nanoparticles obtained are generally distributed between 50-100 nanometers and are composed of titanium and oxygen elements. Besides, it has been observed that the dimensions of some formations can reach 200 nanometers. In conclusion, taking into account the industrial uses as well as the uses in medical fields, the production of TiO2 nanoparticles with biotechnological means using natural sources is a more advantageous option. Moreover, the results of this study contribute to the development of new biological methods that can be used in the synthesis of TiO2 nanoparticles.