The photochromism and electrochemical behavior of a Langmuir-Blodgett (LB) monolayer formed by a novel crown-ether-derived azobenzene derivative (CAD) are reported. The large crown-ether functionality was introduced into the CAD molecule as a spacer to provide enough free volume for azobenzene trans-cis isomerization and also as the hydrophilic head group for LB film fabrication. The CAD molecules formed a stable monolayer at the air\water interface which could also be transferred well to solid substrates. The photochemical conversion rate from trans to cis isomers in this azobenzene monolayer reached 76 +/- 4%, showing a great increase compared with that in a simple long-chain fatty acid azobenzene LB film (30%). It is only a little smaller than the value obtained in solution (86%). The two isomers in the LB films showed significantly different electrochemical responses, with the cis isomer being more easily reduced than the trans isomer. The electron transfer rate constant k(s) was also evaluated. The present studies confirmed that the incorporation of a large group can greatly improve the photochromism of azobenzene in condensed films and demonstrated the great potential of molecular design for controlling the functionality of monolayer assemblies.