Nowadays, one of the environmental problems is spread of waste or side products of industries. Reuse of these wastes can reduce environmental pollution, maintain non-replaceable natural resources, and restores the energy consumed during production of these wastes. One of the most important industrial wastes in Iran is the slag of steel companies, which are the by-product of induction furnaces and contain significant amounts of important elements such as SiO 2 , Al 2 O 3 , FeO and CaO. Slags also have low amounts of MgO, MnO and TiO 2 . Electric Arc Furnace (EAF) slag is a potential raw material for zeolite synthesis. In this study, the synthesis of zeolite A was carried out using acid leaching of slag and adding sodium hydroxide and sodium aluminate to the solid leftover of acid leaching. In this process, sodalite is produced as a byproduct. Zeolite 4A is used in detergents due to its ion exchange capacity, and sodalite is also used in some industries as adsorbent, catalyst, and ion converter catalyst due to its large surface area and large active sites. In all experiments, mass balances of elements were fully considered. In each leaching run, 150 g of pulverized slag was washed with 3600 ml of 8 M acetic acid at 110 o C for 2 h and the solid part was separated by simple paper filtration, followed by leaching the solids with 5000 ml of 5 M hydrochloric acid for 2 h at 110 o C. The final solid was paper filtered and washed with copious DM water, and saved for characterization and zeolite synthesis. To observe silicon to aluminum ratio of one for synthesis of 4A zeolite, 643 ml of sodium aluminate and 102.88 g of 4 M sodium hydroxide was added to the leached slag to prepare gel samples for crystallization. Gel samples were placed in oven for different time intervals for crystallization. After crystallization, the products were separated by paper filtration, washed with DM water and dried; the final product was saved for characterization. XRF, XRD, SEM and EDAX were used for characterization. Atomic Absorption Spectroscopy (AAS) was used to analyze the liquid leftover of acid leaching. Results of AAS tests showed that there exists 1.7 % wt Fe, 0.3% wt Ca, 0.14% wt Al, 0.19 % wt Mg, 0.12 % wt Ti, and 0.0009% wt Mn in the second acid leaching liquid phase. XRF results indicated that the composition of SiO 2 , FeO, and CaO in solid phase of after final leaching was 93.5%, 0.784%, and 0.746% wt, respectively. By analyzing the XRD patterns and Si/Al ratio by EDAX proved the formation of 4A zeolite. XRD patterns showed that sodalite, Bicchulite, TiO2, FeO, and MgO are also present in the final product as impurities. Studies of crystallization time showed that by increasing the crystallization time, the crystal size became larger, and the zeolite phase of sodalite was increased. Material balances showed that the highest conversion of slag to zeolite 4A and sodalite was obtained at crystallization times of 6 and 12 h, respectively. Finally, the collective yield of 38.7 % was achieved for conversion of slag to 4A zeolite and sodalite.