Telechelic cis-1,4-oligoisoprenes were prepared by the selective cleavage of weak epoxidized units (E) in epoxidized cis-1,4-polyisoprenes (EPIs) and by the random cleavage of isoprenic units (I) in cis-1,4-polyisoprene (PI). In both cases, cleavage by periodic acid (H 5 IO 6 ) in tetrahydrofuran led to aldehydic and ketonic chain ends. Through variations in the E/(I ϩ E) molar percentage (E%) in the cleavage of EPI and through variations in the H 5 IO 6 /I molar percentage (PA%) in the cleavage of PI, a polydispersity index near 2 and a number-average molecular weight of 2 -20 ϫ 10 3 were obtained. The correlation of the degree of scission with E% and PA%, combined with kinetic, led to the proposal of a two-step mechanism for the H 5 IO 6 cleavage of double bonds.