Several underground coal mines in Australia have recently reported and anticipated significant floor heave in gateroads during longwall retreat. Floor heave on longwall retreat is typically attributed to a stress notch. To further understand the mechanisms of floor heave, in situ floor heave monitoring was conducted using floor instrumentation at two coal mines. This paper provides the field monitoring results along with the process of selecting the instruments and monitoring sites. To grasp the whole picture of the deformation of floor strata, the instruments for both the vertical and horizontal movements of floor units were considered. For the horizontal floor deformation, the strain gauged shear strips were used in both mines. For the vertical displacement of floor units, a remote reading tell-tale (RRTT) was chosen in Mine A, while a GEL extensometer specifically designed for this floor monitoring was selected in Mine B. As Mine A had negligible floor heave at the monitoring sites, no significant movement of the floor was captured. Although the level of floor deformation was minimal, there were indications of bedding separations as the longwall face approached the sites. In Mine B, minor floor heave was observed at the monitoring location. The data from the instruments showed that the horizontal movement of the floor strata occurred greater than approximately 4 m below the floor surface which may suggest the depth of floor failure. While several practical issues were identified from the field studies, the field monitoring results facilitated better understanding of the failure mechanisms.