We examined the influence of additional external pressure on the optical emission intensity from plasmas produced by laser ablation of a Ti target immersed in distilled water. We adopted two methods for applying the external pressure. When ambient water was pressurized by connecting the ablation chamber to N-2 gas at a pressure range of 0.1-0.9 MPa, we observed the increase in the optical emission intensity with the pressure. This increase was considered to be caused by the change in the amount of dissolved N-2 gas in the water. On the other hand, when an external pressure of 30 MPa was applied to ambient water by using a mechanical pump, we observed the compression of the spatial distribution of the optical emission intensity. These experimental results suggest a possibility that chemical reactions and physical states (pressure and temperature) of liquid-phase laser-ablation plasmas can be controlled by adding external pressure to ambient liquid. (C) 2009 Elsevier B.V. All rights reserved.