Abstract: It was discussed theoretically and tested experimentally that Fe 3 , Mg 2 and Zn 2 could be precipitated completely by ammonium hydroxide and sodium hydroxide, respectively. When ammonium hydroxide was used as precipitant in the catalyst preparation by coprecipitation method, the main components of non chromium iron based catalyst, Fe 3 , Mg 2 and Zn 2 , could not be coprecipitated completely under the same conditions. And this was why the catalyst could not be duplicated easily. As an alternative precipitant,sodium hydroxide was used to prepare non chromium iron based catalyst for oxidative dehydrogenation of n butene to butadiene in co precipitation method. When the precipitate was washed properly, the catalyst prepared by sodium hydroxide showed higher conversion and selectivity than that by ammonium hydroxide used usually. Using cheaper feed and eliminating the feed loss, the cost of the catalyst was reduced in sodium hydroxide technology. The crystal structure and acidity of the catalysts were determined, It was discovered that the sodium in the catalyst reduced its acidity, and this resulted in the decrease of its conversion and selectivity. If the amount of sodium in the catalyst reached a relatively high level, the active crystal structure of the catalyst could not be formed.