The goal of the present study was to produce geopolymers based on flay ash and recycled ladle furnace slag as starting materials. This aim was extended to study the applicability of using these geopolymers as a catalyst for the production of biodiesel. Geopolymers were prepared in multiple batches using fly ash and ladle slag in the presence of an alkali solution. X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR) were used to assess the phase identification of the manufactured geopolymers. The apparent porosity and bulk density as physical properties of the processed materials were evaluated. In addition, a compressive strength test was conducted. A trial was carried out utilizing the calcined geopolymer powders at varying temperatures (110-700 oC), as a catalyst in the production of biodiesel. This process was achieved in the presence of soybean oil and methanol. The kinetic viscosity, flash point, and density of the prepared biodiesel were measured to assess its efficiency. The gained results showed that ladle slag and fly ash could be effectively used to manufacture geopolymer bulk materials. The density and compressive strength of the prepared geopolymers were improved by increasing the fly ash content in the batches. The batch containing 30% fly ash and 70% slag exhibited the highest compressive strength (14.5 MPa) of the developed geopolymers. In addition, the generated biodiesel's viscosity, flash point and density measurements fell within the expected ranges of 2.8-5.1 mm2/s, 90-135 °C and 0.848-0.885 g/cm3, respectively.