This study examined the changes in plant biomass due to fluctuations of rainy season precipitation on Mitchell Grassland in north central Queensland, Australia using MODIS imagery and precipitation records of El Niño and La Niña events. The mostly treeless, about 335,330 sq. km. (slightly smaller than Finland) vast plain is the home for Mitchell Grasslands. About 72% of grassland falls within Queensland where extensive cattle and sheep farming are based. Queensland has about 50% of Australian cattle industry, and feeds nearly 12 million cattle primarily on Mitchell Grass and the sustainability of the grassland is the key efficiency of related economic activities. In this regard freely available MODIS satellite data provides a promising monitoring tool, when the land is homogeneous. This study quantified the changes in biomass according to rainfall recorded in recent El Niño and La Niña events, in a 10,000 sq. km. area in Hughenden, Queensland. In 2002/03, Hughenden Airport observatory recorded an extremely low precipitation (29.4mm) for Nov-Jan rainy months, while 2008/09 recorded an extremely high precipitation (529.0mm). MODIS data were gathered by observing daily rainfall distribution to link the biomass changes of grassland with precipitation fluctuations. The Enhanced Vegetation Index (EVI) calculated using MODIS data shows a significant relation of greenery changes according to precipitation trends, which can be used as a monitoring tool to assess the grassland health. Further research should be conducted on more locations under different precipitation conditions to produce an algorithm for predicting health of the Mitchell Grass Downs Bioregion.