Research objective: To study the retention of magnetic particles in glioblastoma spheroids and to determine their number over a period of 3 weeks. Study design: In vitro study - controlled experiment. Materials and methods: The glioblastoma cell line, D54, was incubated with magnetic nanoparticles at 37°C in a controlled atmosphere, with high humidity and 5% CO2 during 6 hours. 5000 cells were counted, transferred into 24-well plate and covered with a 24-magnet plate. Cells prepared this way were put into the incubator and occasionally, every few days, the media was changed so that the cells would grow successfully. After 7th, 14th and 21st day, the spheroids were cut on a cryostat and then stained with Masson stain. We examined and imaged the sections prepared in this way on a light microscope with a built-in camera. For quantification and obtaining results, images were analyzed using the ImageJ program. Results: The number of magnetic particles reduced over time. A statistically significant decrease is visible between the 1st and 3rd week. The number of magnetic particles decreased, and the amount of empty space increased. In spite of this, we also determined the decrease in the proportion of magnetic particles in the tissue. We also found that the spheroids lose their round shape after a certain time and disintegrate. Conclusion: The magnetic levitation method is a frequently used method in the formation of spheroids. The magnetic particles used for this method remain in the cells only for a certain period of time. The number of magnetic particles correlates with time, meaning that, as time goes on, their number is reduced. As a result, the spheroids begin to disintegrate and form irregular shapes.