Abstract This paper presents the strength effect of the F mineral admixture (FMA) which is made of the finely divided powder of natural Zeolite Rock ground with a bit of other inorganic material. Test results indicate that a concrete mixing with 450 kg/m 3 of ordinary portland cement (OPC), 50 kg/m 3 of FMA and W C (= W C + FMA)=355 can have a compressive strength above 80 MPa, while the compressive strength of the corresponding concrete mixing with 500 kg/m 3 of OPC is only 70 MPa. Test results also conclude that, when a 5–10% of cement in the concrete is displaced by FMA under the condition of using superplasticizer (HRWR) and W C =0.31−0.35 , the strength if this concrete is 10–15% higher than that of the corresponding concrete mixing with pure OPC. The mechanism of strengthening effect on concrete strength by FMA is also studied and discussed. This strengthening effect by FMA occurs only at lower water-cement ratio with HRWR and fineness of FMA lower than that of cement. The strengthening effect of concrete by FMA to slag portland cement concrete is also similar.