We have performed the study of microscale/nanoscale plasma science and technology.@footnote 1@ In this talk, our recent work on microdischarge plasma in supercritical fluid (SCF), particularly near the critical point (CP), for CO@sub 2@ (CP:7.38MPa,304K)and H@sub 2@O (CP:22.1MPa,674K), are presented. SCF,which is an intermediate state of matter between liquid and gas, has attracted much interest in scientific and enginering fields due to abnormal characteristics, such as high solubility. In particular, near CP, large density fluctuation results in drastic change of the properties. From a microscopic viewpoint, the SCF consistes of various sized clusters. Therefore, it is highly anticipated that the ionized state, such as the plasma state, in SCF may exhibit unique characteristics and reactions, that are distimct from those of the normal plasma state in gas. In addition to the first generation@footnote 2@ of plasma in SCF, abnormal features of breakdown voltages (V@sub B@) as a function of environmental pressure are demonstrated. For CO@sub 2@, measurements of V@sub B@as a function of pressure for high-pressure CO@sub 2@ up to SCF conditions of various temperatures have been performed using a 1-µm-gap coplanar film electrode. The curve of the V@sub B@ exhibits an inflection at around 3 MPa and a drastic decrease near CP. The V@sub B@ in pressure environments higher than the inflection at around 3 MPa can be analyzed using the Townsend theory and density fluctuations, which typical indicates clustering, and the drastic decrease of V@sub B@ near CP was shown by a scaling function. The same features were also observed for H@sub 2@O. Finally, as an example of an application, the preparation of carbon-cluster systems, such as nanopolyhedra and nanotubes, using SCF-CO@sub 2@ plasma is also presented. @FootnoteText@ @footnote 1@ K.Terashima, L.Howald, H.Haefke and H.J.Güntherodt, Thin Solid Films 282(1996)634. @footnote 2@ T.Ito and K.Terashima, Appl.Phys.Lett.80(2002)2854.