Abstract: The high temperature tensile creep tests were performed on TiB₂ ultrafine particulate reinforced ZL109 composite prepared by in situ formation technique. The composite exhibits high values of apparent stress exponent and apparent creep activation energy under constant applied stress at elevated temperatures. These values exceed greatly those forpure aluminum and ZL109 alloy. High temperature creep properties of the in situ TiB₂/ ZL109 composite are better thanthose for conventional particulate reinforced composites. By introducing a threshold stress , the creep results of the composite can be explained by a microstructure invariant model , implying that creep of the composite is controlled by lattice diffusion in the matrix. The creep rupture behavior of the composite can be represented by Monkman-Grant empirical equationand the rupture characteristic of the composite is ductile fracture.