Glioblastoma (GBM) is a highly aggressive brain tumour characterized by a complex tumour microenvironment (TME) that interacts intricately with immune cells. This study aimed to develop a GBM-on-chip model to investigate the interactions between the tumour and its microenvironment in a controlled system, particularly with microglial cells, which are the resident immune cells of the brain. A microfluidic device was fabricated in polydimethylsiloxane (PDMS) using microfabrication, to mimic the structural and functional characteristics of the GBM TME. The chip comprised separate compartments for cerebral vasculature and brain parenchyma, facilitating the observation of cellular behaviours and interactions. To assess the microglial response to the tumour environment, we focused on the phenotypic transition of microglia from the pro-inflammatory M1 state to the anti-inflammatory M2 state.