By measuring electrical conductivity (EC),the time it takes for ions to reach equilibrium in reaction in the soil-water system was investigated.The EC-time curves of 20 soil suspensions (30 g kg^-1) prepared out of 5 tested soils and 4 nitrate solutions of 10^-4/3z mol L^-1 showed that ECs of the suspensions all decreased until the ion reaction reached equilibrium after 100~300 hours.The curves of Wien effect of two yellow-brown soil suspensions (10 g kg^-1) that contained 10^-4mol L^-1 Cu(NO₃)₂ and Pb(NO₃)₂,respectively,varied with the equilibrium time in location and shape,and overlapped when the equilibrium time reached or exceed 480 hours.The EC value of suspensions (10 g kg^-1) of yellow-brown soil containing 2 10^-4mol L^-1 NaNO₃ and KNO₃ and the concentrations of Na⁺ and K⁺ions in their supernatants showed a similar tendency at first and reached equilibrium after 70 hours and 30 hours,respectively.These experimental results show that conductometry is indeed a simple means to determine time it takes for ions to reach equilibrium in reaction in the soil water system.