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Graywacke samples from the Flagstaff Formation having a mean uniaxial compressive ( σ_m) strength of 185 MPa were subjected to cyclic load tests in order to investigate their fatigue and strain hardening behaviours. A fatigue stress of 87% (i.e. 161 MPa) and strain hardening up to 29% (i.e. 239 MPa) were determined for these samples. It was also established that with decreasing stress amplitude the fatigue life of a rock increases. With another set of experiments it was determined that the strain hardening percentage increases up to a limit with an increasing number of load cycles. This means that the strain hardening percentage of a sample subjected to 500 load cycles (below fatigue stress) will be more than that of an identical sample having been subjected to only 100 load cycles under the same conditions. It was further established that a sample having suffered cyclic loading with a higher value of maximum …