A method of mass-spectrometric sampling (MSS) of solid propellant (SP) flames for SP flame structure investigation is described. Two types of instruments have been developed: 1) microprobe sampling and 2) molecular-beam mass spectrometry (MBMS), using time-of-flight mass spectrometry (TOFMS). Addressing an important question concerning estimated errors of probe measurements, detailed investigations on substantiating the sampling technique for flames with narrow combustion zones have been carried out. Examples of the mass-spectrometric probing technique applications to study the flame structure of the following solid propellants and their ingredients are presented: RDX, HMX, sandwich type systems based on HMX and double-base propellants. Applications of MSS to study of unstable combustion of SP are described.