MassChroViewer tool is released. This is a 2-Dimensional data viewer for quality checking of LC-MS data. Retention time, m/z, and intensity of the ions in raw data (mzXML format) are visualized as x-axis, y-axis and strength of color. Zooming in/out and moving of the view area can be changed as Google-Map like mouse operations. The functions for overlay the extracted peaks, checking mass differences, MS/MS data browsing, compound database searching, browsing chemical structure of candidate compounds, and mass calculation of selected substructure can be used to check the quality of raw data and processed data.