U ovom je radu istražena mogućnost primjene niskotemperaturnih eutektičkih otapala za ekstrakcijsku deacidifikaciju otpadnih životinjskih masti te uklanjanje glicerola i glicerida iz sirovog biodizela. Istraživanje je uključilo odabir povoljnog katalizatora te masenog omjera katalizatora, metanola i masti koji bi rezultirali najvećom konverzijom triglicerida u metilne estere masnih kiselina. Definirano je potrebno vrijeme pročišćavanja sirovog biodizela te optimalan maseni omjer otapala i sirovog biodizela. Ekstrakcijskom deacidifikacijom pomoću niskotemperaturnog eutektičkog otapala na bazi kalijeva karbonata uspješno je reducirana kiselost sirovine uz relativno mali utrošak otapala (maseni omjer otapala i masti: 0,25 : 1,00) i kratko vrijeme trajanja procesa (30 min). Kalijev hidroksid pokazao se kao učinkovitiji katalizator. Udio katalizatora u reakcijskoj smjesi utječe više na konverziju masti od udjela metanola. Udio glicerola i glicerida reduciran je ekstrakcijom pomoću niskotemperaturnog eutektičkog otapala na bazi kolin klorida na vrijednosti manje od standardom propisane vrijednosti (EN 14214:2019). Odabrano se otapalo pokazalo selektivnim zbog toga što nije došlo do redukcije udjela metilnih estera. Pri masenom omjeru otapala i biodizela 1 : 1 i 90 min trajanja ekstrakcije postignuti su najbolji rezultati. Pročišćeni biodizel također zadovoljava standard kvalitete s obzirom na udio estera, gustoću i viskoznost.; Given the fact that biodiesel produced from oil used in the food industry is not competitive with fossil-based diesel, it is necessary to use cheaper raw materials for its production. Thereby, waste edible oil, by-products of the manufacturing process of edible oils, inedible oils, and waste animal fat are considered the economically acceptable raw materials. The goal of this work was to investigate the applicability of deep eutectic solvents for extractive deacidification of waste animal fats and removal of glycerol and glycerides from crude biodiesel. Extractive deacidification of waste animal fat was conducted using deep eutectic solvent potassium carbonate – ethylene glycol (1 : 10, mol.), and it was used in mass ratio 1 : 4 (solvent : fat), at 60 °C for 30 min. Total acid number was reduced from 26.63 to 1.1 mg KOH/g fat. After purification of the feedstock, biodiesel was synthesised with different catalysts (KOH and NaOH), and KOH exhibited better conversion; therefore it was chosen for further experiments. In order to define the optimal reaction conditions, the influence of mass ratio catalyst : methanol : fat on the conversion of triglycerides into fatty acid methyl esters was investigated. At all reaction conditions, high quality biodiesel was obtained, i.e., the ester content was above the EN 14214 limit (96.5 %). The influence of catalyst load was greater than of methanol. At the highest concentration of catalyst, neutralisation of free fatty acids occurred. Biodiesel synthesised at 1 : 40 : 100 (KOH : methanol : fat) was chosen as the best, and was used for further experiments – extraction of glycerol and glycerides from crude biodiesel. For that purpose, deep eutectic solvent choline chloride – ethylene glycol (1 : 2.5, mol.) was used. The influence of mass ratio solvent : biodiesel and extraction duration was investigated. Increase in mass ratio and extraction duration resulted in a slight increase in ester content.