MSSTYLES is a file extension characteristic of the older Windows XP operating system. MSSTYLES are files used to store styles for the system. Such files made it possible to customize the graphical user interface according to his preferences. Such a file could change the shape and size of individual elements of the system and adjust its colors.

MSSTYLES files were pre-installed with the system, but users could load their files onto the system using the StyleXP utility. Currently, Windows XP and the MSSTYLES format are less and less common and are considered obsolete.