One of the problems of recycled concrete aggregate (RCA) is the lack of sufficient adhesion between aggregates and the cement paste, which leads to a decrease in mechanical strength and an increase in concrete permeability. Besides, steel fiber (SF), due to creating greater continuity, and magnetite powder (MP), with its filling property, can enhance the mechanical properties and durability of concrete. It seems that by using SFs and MP in RCA, its mechanical properties and durability can be improved. The aim of this study is to investigate the effects of using SFs and MP on the mechanical properties, durability, and microstructure of concrete containing 30% by volume of recycled aggregate obtained from crushing concretes with different strength grades, replacing natural coarse aggregate. SFs at 1% by volume of concrete and MP at 5%, 10%, and 15% as a replacement by weight of cement were used. The mechanical properties of RCA were evaluated by compressive and flexural strength tests, and the durability of concrete was evaluated by the water absorption test at the age of 28 days. Furthermore, to examine the concrete microstructure, scanning electron microscopy (SEM) imaging was used. In addition to normal temperature conditions, all tests were also performed on concrete specimens subjected to high temperatures including 200, 400, and 600 degrees Celsius to investigate the effectiveness of SFs and MP in compensating for the loss of concrete strength at high temperatures. The experimental results showed that adding SFs and 10% MP to RCA increased compressive and flexural strengths by 15% and 10%, respectively, and also reduced the water absorption rate by 8%. Furthermore, adding 10% MP to the concrete reduced the compressive strength loss of concrete under 600 degrees Celsius from 38% to 19%. Based on SEM images, adding MP to concrete increased the density of its microstructure.