Self-assembled chitin nanofibers were applied as a biomimetic extracellular matrix for the attachment of primary neurons in vitro. Chitin nanofiber surfaces were deacetylated to form 4 nm and 12 nm diameter chitosan nanofibers that were coupled with poly-D-lysine (PDL) to examine combinatory effects and structurally analyzed by atomic force microscopy. The chitosan substrates were then employed for mouse cortical neuron cultures to examine their capabilities to support cell attachment, neurite coverage and survival. The 4 nm chitosan nanofibers improved single cortical neuron attachment compared to the 12 nm chitosan fibers and bare glass substrates, illustrating the improved adhesive properties of the surface. Importantly, the 4 nm chitosan nanofibers with PDL supported 37.9% neuron viability compared to only 13.5% on traditional PDL surfaces after a 7-day culture period, illustrating significantly improved long-term cell viability. The nanofibrillar chitosan surface could provide an alternative substrate for in vitro primary neuron cultures to serve as artificial neural networks for diagnostics and therapeutics.