© 2019, Institute of Electrostatics. All rights reserved. Microplasma discharges in deionized water and artificial seawater were investigated using pin-to-plate electrodes with a gap of a several tens of microns. By using a pulse voltage source, microdischarge was operated in deionized water and diluted artificial seawater and compared with discharge in ambient air. To operate the microdischarge in undiluted artificial seawater, a pulse current source (impulse generator) was used to supply the breakdown voltage with sufficient current. Even in seawater with an electrical conductivity of 45 mS/cm, microplasma discharges were reproducibly ignited at applied voltages below 1 kV. In the optical emission spectrum for the microplasma in artificial seawater, the main components of Na, Mg, Ca, K, S, H, and O were observed as distinguishable isolated lines, including lines for Pd, Ag and Fe from the electrodes.