The technique of time resolved microwave dielectric absorption has been used to study the excited triplet states formed by the laser flash photolysis. The details of the experimental method and apparatus are discussed. The triplet state lifetimes and triplet state dipole moments of fluorenone and its derivatives are reported. The triplet state lifetime of fluorenone agrees with that obtained by optical absorption. The lifetime measurements with argon purging and with air equilibrated solution confirm the formation of triplet states. A marked increase in the triplet state dipole moment of fluorenone and its derivatives is observed and implies that their lowest triplet state is of (π, π*) in nature.