A novel azo pyridinium compound, 4-[(2-hydroxyl-5-methylphenyl)azo]-1-octadecylpyridinium iodide (HAPO), and its analogue, 4-[(2-hydroxyl-5-methylphenyl)azo]-1-methylpyridinium iodide (HARM), were synthesized, and their photochromic and electrochemical behaviors were studied both in solutions and in Langmuir-Blodgett films. Reversible photochromism through a photothermal cycle and a good reversible oxidation/reduction process were observed. The reaction of HAPO in solution undergoes a first-order kinetic process. The mechanisms of photochromism and oxidation/reduction were also proposed. Data show this new compound is an ideal material for information storage.