The permanent deformations of unbound pavement layers are typically caused by the movement and densification of aggregate particles under the influence of repeated wheel loads. This type of distress, which represents one of the major failure modes in flexible pavements, has been investigated by many researchers. In this research, a miniaturized pressuremeter (MPMT) device was used to predict rutting of unbound granular materials by performing cyclic field testing. The permanent deformations measured using cyclic triaxial (CT) testing were compared with those predicted from the MPMT testing. Four unbound pavement materials used as a pavement base and subgrade were tested and evaluated. The Tseng-Lytton model, also known as the sigmoidal model, was used to analyze and interpret permanent strain data obtained from both tests. The data showed that the permanent strains predicted from in situ MPMT tests are larger than those measured from laboratory CT tests. However, it is demonstrated that the best results are obtained when MPMT permanent strains are adjusted by using the slope of the strain level model as a reduction factor. The results indicated that the average ratio of predicted to measured permanent strain was 0.66 and 0.89 for subgrade and base course materials, respectively. In addition, it was concluded that the MPMT stress-strain data from ten MPMT loading cycles provide a reasonable estimation for soil strain parameters of the sigmoidal model.