Acid clay treatments are well known for their performances in the treatment of used lubricating oils. Based on different experimental factors, a new technology will develop using acid clay treatment process for the recovery of used lubricating oil. This research investigates the effect of two different acids (hydrochloric acid and acetic acid) followed by treatment with different mixing time (1 hour and two hours), settling time (24 hours and 48 hours), neutralizing base (sodium hydroxide and ammonium hydroxide) and deposits of clay from sululta and melka jebdu having different chemical and physical characteristics. Filtration, heating, and washing were carried out on treatment procedure to improve the quality of the used engine oil. To compare the results obtained with these treatments, specific gravity/ density, kinematic viscosities, water content, total acid number, total base number, ash content, flash point, pour point and metal contents of fresh oil and used oil have been analyzed. The results from the test showed, varied degrees of improvements on the properties of treated oil which depends on the experimental factors. And the optimum result was obtained at 2 hours mixing time and 48 hours settling time with a viscosity of 85.85 cst at 40 ⁰C, viscosity of 10.6 cst at 100 ⁰C, ash content of 0.299 %, pour point of -12 ⁰C, and flash point of 204.5⁰C ; melka jebdu clay with a TAN of 2.51 mgKOH/g, TBN of 6.37 mgKOH/g, water content of 0.010 %, cadmium metal of 0.06 ppm, and copper metal of 0.31 ppm; strong base neutralization with a Total Acid number of 3.81 mgKOH/g and Total Base Number of 5.56 mgKOH/g ; and weak acid break down with a specific gravity of 0.869. But strong acid break down has a good effect on the concentration of metals found in the treated engine oil. The experiments showed that the acid-clay treatment process was good in recovering valuable oil from used oil samples with comparable qualities. Key words: used engine oil, fresh oil, clay, acid clay treatment.