Gas injection into melt contained in ladle through porous plug is a useful technique for homogenizing temperature distribution and chemical composition of molten steel. Performance of the gas injection process depends on the gas flow rate, porous plug location and alloy addition position. In the present work, the effects of gas flow rate, depth of melt, position of tracer injection, and slag layer on mixing time for a ladle with capacity of 40 tones whose porous plug located in 0.63R was investigated. Experiments were carried out by bottom injection of Ar gas into the water model, and silicone oil was used as top slag layer. Mixing time for presence as well as absence of oil layer was investigated in different gas flow rates and various bath depths for tracer injection at slag eye and opposite slag eye position. Moreover, the effect of gas flow rate, alloy addition position, and slag layer on the dissolution rate of alloying elements was investigated using cylindrical specimen of benzoic acid. According to the obtained results for oil absence condition, when the tracer injected at slag eye, the maximum mixing time occurred in minimum bath depth (30 cm) for each gas flow rate. Also the mixing time decreased from 86.6 to 61.8 s with increasing gas flow rate from 3 to 6.75 L/min. For each gas flow rate, the minimum mixing time occurred at the maximum bath depth (45 cm), thus the mixing time decreased from 77.6 to 56.2 s with increasing of the gas flow rate from 3 to 6.75 L/min. When the tracer was injected at slag eye and in the presence of oil layer with 0.1L thickness, the mixing time was increased 75 to 107%. However, in the absence of oil layer when the tracer was injected at opposite slag eye position, the maximum mixing time occurred at minimum bath depth (30 cm) for each gas flow rate. Also the mixing time decreased from 109.25 to 74 s when gas flow rate increased from 3 to 6.75 L/min. For each gas flow rate, the minimum mixing time occurred at the maximum bath depth (45 cm), thus the mixing time decreased from 94.8 to 62.6 s with increasing of the gas flow rate from 3 to 6.75 L/min. The mixing time increased from 80 to 100% when the tracer was injected at opposite slag eye position in the presence of oil layer with 0.1L thickness. An empirical correlation was suggested for the mixing time for each position of tracer injection. The results of dissolution rate measurements of benzoic acid specimens indicated that the dissolution rate in plume is higher than in the case of opposite position of plume, and the presence of oil layer with0.1L thickness, led to decrease of dissolution rate. Finally, according to the secondary steelmaking parameters in ladle furnace in Iran alloy steel company, the optimum conditions were suggested for homogenizing molten steel by injecting of Ar gas. Keywords: Mixing time, Gas injection, Gas stirred ladle, Homogenizing molten steel, Dissolusion of alloying elements, Entrapment of Slag.