To precipitate the complex gels of the pH 6, 7, 8, 9 included in a flux and an aluminum hydroxides gel, an aqueous solution of a mixture of $Na_2CO_3;and;Na_2PO_4{cdot}12H_2O$ was added with stirring in an aqueous solution of a mixture of $Al_2(SO_4){_3}{cdot}18H_2O,;Na_2SO_4;and;K_2SO_4$, and then the complex gels were aged in 20 h at $90^{circ}C$. As the hydrolysis pH changed, it had an effect on the physical properties such as the crystal structure, crystal morphology and a phase transition temperature of the AlO(OH) gel, and also on the crystal structure, crystal morphology, particle size and particle size distribution of the ${alpha}-Al_2O_3$ platelets prepared by molten-salt precipitation. Also, in this study, the complex gels were crystallized at $1,200^{circ}C$ and thereafter dried at $110^{circ}C$, and then it was investigated to effect of the hydrolysis pH on the crystal structure, morphology and particle size distribution of the ${alpha}-Al_2O_3$ platelets crystals using XRD, DTA, SEM and particle size analyzer.