Experimental investigations are carried out on mixing time in a water bath agitated by side gas injection with an L-shaped lance. The mixing time is measured using an electrical conductivity sensor and an aqueous KCl solution as a tracer. Particular attention is paid to bath agitation under the conditions that any kinds of swirl motions of a bubbling jet do not appear. An empirical equation is proposed for the mixing time as a function of the gas flow rate, bath diameter, bath depth, and the physical properties of water by referring to a previously proposed empirical equation for mixing time in a bath agitated by J-shaped top lance gas injection. The equation is compared with an empirical equation proposed for a bath in the presence of a swirl motion of the deep-water wave type.