NOVELTY - A carbon-based magnetic solid alkali catalyst is prepared by mixing press carbon powder, metal cation, precipitating agent and water to form mixture (a), reacting mixture, filtering, washing and drying mixture to obtain mixed precipitate, calcining mixed precipitate to obtain carbon-based magnetic support material, mixing carbon-based magnetic support material, Portland cement and water to form mixture (b) and pressing mixture (b), evaporating mixture (b) to form jelly, calcining jelly at 300-500 degrees C for 2 hours, grinding calcined mixture and sieving mixture.    USE - Carbon-based magnetic solid alkali catalyst is used for production of biodiesel (claimed).    ADVANTAGE - The carbon-based magnetic solid alkali catalyst having excellent catalytic efficiency is economically prepared, by simple method.    DETAILED DESCRIPTION - A carbon-based magnetic solid alkali catalyst is prepared by mixing press carbon powder, metal cation, precipitating agent and water in molar ratio of 21-101:12:30:350 to form mixture (a), reacting mixture at 100-150 degrees C for 1-12 hours, filtering, washing and drying mixture to obtain mixed precipitate, calcining mixed precipitate at 400-1000 degrees C for 1-5 hours to obtain carbon-based magnetic support material, mixing carbon-based magnetic support material, Portland cement and water in mass ratio of 1:1-5:15 to form mixture (b) and pressing mixture (b), evaporating mixture (b) at 85-105 degrees C for 1-10 hours in rotary evaporator to form jelly, calcining jelly at 300-500 degrees C for 2 hours, grinding calcined mixture and sieving mixture to form carbon-based magnetic solid base catalyst of 200 mesh. The metal cation comprises ferric nitrate, cobalt nitrate and/or nickel nitrate. The precipitation agent comprises urea, ammonia, sodium hydroxide and/or potassium hydroxide. The silicate is sodium silicate and/or potassium silicate. An INDEPENDENT CLAIM is included for usage of carbon-based magnetic solid alkali catalyst for production of biodiesel.