Fly ash is the residue from combustion of coal that currently being used as adsorbent for heavy metals and inorganic compounds from aquatic system. One of the inorganic compounds that can be adsorbed by fly ash is phosphate. The abundance of phosphate compounds can lead into eutrophication that contribute to a serious problem in aquatic ecosystem. So, the handling of this problem is needed. In this study, fly ash was modified with hydrothermal method to form a fly ash zeolite. The zeolite was mixed with magnetite (Fe3O4) with ratio 3:1 to form a magnetic adsorbent. X-Ray Fluorescence and X-Ray Diffraction pointed that the fly ash contains Si/Al as the main elements. The ratio of Si/Al after modification with magnetite is 2.22. Fourier Transform Infrared spectroscopy analysis indicated that the type of zeolite after synthesized is hydroxysodalite. Scanning Electron Microscopy images showed the cluster of small particles analyzed as magnetite that attached to the surface of zeolite. The adsorbent from fly ash will be used to adsorb phosphate from aquatic system. Phosphate adsorption from fly ash adsorbents was studied on various parameters, namely adsorbent amount, pH, contact time, and initial phosphate concentration. The result from this study showed that fly ash modified with magnetite has the highest adsorption capacity and efficiency that is of 2.24 mg P/g and 90.42 %. The optimum conditions were obtained at pH 3 and contact time within 120 min. Magnetite particle addition effectively increased the separation of adsorbent containing phosphate and supernatant using magnetic field. This study highlights that byproduct from fly ash can be applied to reduce phosphate concentration in aquatic system.