This study assesses the potential of regional microwave backscatter data assimilation (DA) in AquaCrop for the first time, using NASA’s Land Information System (LIS). Soil moisture and crop biomass simulations from AquaCrop were updated using Sentinel-1 synthetic aperture radar (SAR) observations, over three regions in Europe. This was done in two separate DA experiments. The first experiment concerned updating soil moisture using VV-polarized backscatter and the corrections were propagated via the model to the biomass. In the second experiment, the DA setup was extended by also updating the biomass with VH-polarized backscatter. The assimilation showed mixed results, with slight overall improvements in the (anomaly) correlations of soil moisture simulations relative to independent satellite and in situ data. By contrast, the biomass estimates obtained with backscatter data assimilation did not agree better with reference datasets from independent optical and microwave satellite data. Given the complex backscatter response over agricultural areas, more research is required to optimally perform DA to improve crop growth estimation.