A new method for controlling perpendicular coercivity of iron electrodeposited alumite films was developed. It was found that addition of sodium hypophosphite in an iron plating bath greatly decreases the coercivity of the iron electrodeposited alumite films, which made it possible to control the coercivity in a range between 500 Oe and 1000 Oe even in the case that the pore diameter is as small as 250A. TEM observations revealed that each acicular iron particle grown in the alumite pore changed from single crystalline state to polycrystalline state by containing small amount of phosphorus. It is considered that the decrease in the coercivity by containing phosphorus is mainly due to the crystallographic discontinuity within each acicular iron particle.