Methylcyclopentane was reacted under low conversion conditions on various plant equilibrated and laboratory steam dealuminated commercial, rare earth exchanged, Y zeolite FCC catalysts at reaction temperatures of 450 to 510 degrees C. Reaction products included mainly C-5- compounds as well as methylcyclopentene, saturated open chain C-6 isomers, C-6 alkenes, C-5 to C-8 cyclic, and aromatic compounds. The reaction is sensitive to catalyst properties, as well as a good probe to evaluate various reactions typical of FCC, like cracking, isomerization and hydrogen transfer, both total catalyst acidity and zeolite unit cell size being necessary to ascertain catalyst performance. The same trends were observed on all the samples. The extension of the reactions following single active site mechanisms (cracking and isomerization) correlated with total catalyst acidity. Reactions obeying mechanisms that demand paired active sites (hydrogen transfer) can be accounted for more properly on a zeolite unit cell size basis. Hydrogen transfer decreases significantly at unit cell sizes lower than 24.30 Angstrom. Lower temperatures favored both isomerization and hydrogen transfer against cracking. The reaction could be used as a test to provide complementary information for commercial catalyst evaluation procedures.