Physical conditions of the decay instability of kinetic Alfven waves in the loop plasma at the early stage of the flare process are investigated. By means of the synchronism conditions a modified expression is obtained for the nonlinear growth rate of the process of the decay of the original kinetic Alfven wave (KAW) into an ion-acoustic wave and secondary KAW. The threshold values are calculated for the amplitude of original KAW in the “background” magnetic field intensity units at the chromospheric part of the loop current circuit. Alfven wave,preflare plasma