To precipitate the complex gel of flux and aluminum hydroxides gel, aqueous solution of the mixture of $Na_2CO_3;and;Na_2PO_4{cdot}12H_2O$ was added with stirring in aqueous solution of the mixture of $Al_2(SO_4)_3{cdot}14{sim}18H_2O,;Na_2SO_4$, and then the complex gel was aged in $0{sim}30h;at;90^{circ}C$. As aging time passed, the aluminum hydroxides was grown into the acicular AlO(OH) gel. Also, aging time had an effect on physical properties of the AlO(OH) gel and on crystal growth of the flaky ${alpha}-Al_2O_3$ prepared by molten-salt precipitation. In this study, the complex gel was crystallized in temperature range of $400{sim}1,200^{circ}C$ after drying at $110^{circ}C$, and then it was investigated to effect of aging time on precipitation temperature, size, thickness, morphology and particle size distribution of the flaky ${alpha}-Al_2O_3$ crystal. As aging time passed, the flaky a${alpha}-Al_2O_3$ crystal showed a tendency toward an increase in size and thickness as result from an increase in BET surface area and pore volume of the acicular AlO(OH) gel.