Rickettsia felis is a rickettsial pathogen primarily associated with the cat flea, Ctenocephalides felis. Although laboratory studies have confirmed that R. felis is maintained by transstadial and transovarial transmission in C. felis, distinct mechanisms of horizontal transmission of R. felis among cat fleas is undefined. Based on the inefficient vertical transmission of R. felis by cat fleas and the detection of R. felis in a variety of hematophagous arthropods, we hypothesize that R. felis is horizontally transmitted between cat fleas. Towards testing this hypothesis, flea transmission of R. felis via a bloodmeal was assessed weekly for four weeks. Rhodamine B was used to distinguish uninfected recipient and R. felis-infected donor fleas in a rickettsial horizontal transmission bioassay and quantitative real-time PCR assay was utilized to measure transmission frequency; immunofluorescence assay also confirmed transmission. Female fleas acquired R. felis-infection more readily than male fleas after feeding on a R. felis-infected bloodmeal for 24 h (69.3% and 43.3%, respectively) and both Rickettsia-uninfected recipient male and female fleas became infected with R. felis after co-feeding with R. felis-infected donor fleas (3.3-40.0%). Distinct bioassays were developed to further determine that R. felis was transmitted from R. felis-infected to uninfected fleas during co-feeding and copulation. Vertical transmission of R. felis by infected fleas was not demonstrated in this study. The demonstration of horizontal transmission of R. felis between cat fleas has broad implications for the ecology of R. felis rickettsiosis.