Cultured neuronal networks are very useful for studying fundamental mechanisms associated with nervous system development and functioning. We have investigated network development and synchronized burst activity of neuronal cells cultured on multi-electrode arrays (MEAs). Using immunofluorescence staining, we measured excitatory and inhibitory synapse densities during 1-month development of cultured rat cortical networks. We also cultured the neurons on MEAs at different densities to investigate minimum network size required for synchronized bursts. In addition, we performed neuronal cell patterning on MEAs to control the network construction. In this review, our recent findings published in some papers are presented.