For an odd prime p ? 5, the structures of cyclic codes of length 5ps over R = Fpm + uFpm (u2 = 0) are completely determined. Cyclic codes of length 5ps over R are considered in 3 cases, namely, p ? 1 (mod 5), p ? 4 (mod 5), p ? 2 or 3 (mod 5). When p ? 1 (mod 5), a cyclic code of length 5ps over R can be expressed as a direct sum of a cyclic code and ?ps i -constacyclic codes of length ps over R, where ?ps i = ?i(pm?1)ps/10, i = 1,3,7,9. When p ? 4 (mod 5), it is equivalent to pm ? 1 (mod 5) when m is even and pm ? 4 (mod 5) when m is odd. If pm ? 1 (mod 5) when m is even, then a cyclic code of length 5ps over R can be obtained as a direct sum of a cyclic code and ?ps i -constacyclic codes of length ps over R, where ?psi = ?i(pm?1)ps/10, i = 1,3,7,9. If pm ?/ 4 (mod 5) when m is odd, then a cyclic code of length 5ps over R can be expressed as a direct sum of a cyclic code of length ps over R and an ?1 and ?2-constacyclic code of length 2ps over R, for some ?1, ?2 ? Fpm\{0}. If p ? 2 or 3 (mod 5) such that pm ?/ 1 (mod 5), then a cyclic code of length 5ps over R can be expressed as C1 ? C2, where C1 is an ideal of R[x]/?xps?1? and C2 is an ideal of R[x]/(x4+x3+x2+x+1)ps ?. We also investigate all ideals of R[x]/?(x4+x3+x2+x+1)ps ? to study detail structure of a cyclic code of length 5ps over R. In addition, dual codes of all cyclic codes of length 5ps over R are also given. Furthermore, we give the number of codewords in each of those cyclic codes of length 5ps over R. As cyclic and negacyclic codes of length 5ps over R are in a one-by-one equivalent via the ring isomorphism x ? ?x, all our results for cyclic codes hold true accordingly to negacyclic codes.