In this study, an investigation was conducted on the effect of cryogenic heat treatment on the wear behavior of AZ91 magnesium alloy using pin-on-disc in a dry and isotonic solution (0.9 wt% NaCl) medium. The wear performance was investigated under loads of 1 N, 3 N, and 5 N. The analysis of the variance method was performed to find the relationship between parameters. The results from the experiment showed that the new microstructure of treated AZ91 was composed of less eutectic phase around b phase and the formation of twinphase was noticed compared to untreated AZ91. The wear analysis demonstrated that in dry and wet medium abrasion and adhesion mechanisms were dominant. Although the untreated sample exhibited better wear resistance in the dry medium, the cryogenically treated sample was better in the wet medium when compared to the wear zone. In addition, the pitting corrosion was observed for all samples in the wet medium; the treated sample had encountered severe pitting compared to the untreated sample. Moreover, the specific wear rate of the treated sample was better than the untreated sample at the wet medium. The coefficient of friction (COF) of the untreated sample was between min. 0.32 and max. 0.54 and higher than the treated sample in the dry medium. However, the COF value of the wet medium was less than a dry medium for all samples and was around 0.24. In general, the treated sample performed better wear resistance in wet medium and was limited at dry mediumdepending on the applied load.