The poor quality of Kenyan in situ concrete has necessitated research to establish the properties of the ingredient materials and their influence on the troubling rate of failure of reinforced concrete structures in the country during construction and usage. The compressive strength of concrete relies on the properties of the constituent materials, proportions of the mixture, workmanship, compaction method and curing conditions. This paper outlines findings of an experimental investigation on the properties of Kenyan concrete ingredient materials and their influence on the compressive strength of concrete in Kenya. Three types of cements (42.5N, 32.5R, 32.5N) from six different cement manufacturers and fine aggregates from three different regions in the country were used during the study. Cements and aggregates chemical analysis was done using the Atomic Absorption Spectrometer machine while the physical and the mechanical properties were checked based on the British Standards. The British DOE concrete mix design method was used to generate the concrete mix proportion and concrete was tested for early and ultimate compressive strengths at 7, 14 and 28 days. It was observed that the different cement brands have varying properties with CEM A having the highest ultimate compressive and flexural strengths. It was further noted that aggregates from the coastal region produced concrete of higher compressive strengths. When the commonly used mix design method was adopted, blended Portland cements produced concrete with ultimate compressive strengths lower than the designed target strengths. The study therefore recommends the development of a concrete mix design procedure for blended cement concrete production in Kenya.