In this paper, the effects of three main preparation factors (pH of the precipitation, aging time and calcination temperature) were investigated on the structural and catalytic properties of mesoporous nanocrystalline magnetite based catalysts in HT-WGS (high temperature water gas shift) reaction. The catalysts were characterized by powder X-ray diffraction (XRD), Brunauer-Emmett-Teller method (BET), temperature-programmed reduction (TPR) and scanning electron microscopy (SEM) techniques. The XRD analysis confirmed the preparation of catalysts directly in active magnetite phase. The results revealed that increasing pH value and decreasing in calcination temperature increased the BET surface area and improve the catalytic activity. However, for the aging time there is an optimum point. It was found that the catalyst prepared at pH value of 10 under aging time of 5h and calcined at 400 degrees C possessed the highest activity compared to the other prepared catalysts. In addition this catalyst showed the higher activity compared to the commercial one. This catalyst exhibited high stable catalytic performance during 20 h time on stream in high temperature water gas shift reaction.