This article highlights the melt crystallization behavior of different grades of isotactic polypropylene (iPP) using a hot-stage polarizing optical microscopy. iPP samples were heated up at a heating rate of 10 degrees C/min passing the melting temperature and then kept for 3 min at a temperature range of 175-200 degrees C before they cooled rapidly at 40 degrees C/min to crystallize isothermally at a range of 130-145 degrees C. It has been found that the temperature at which the samples were kept has a strong effect on the crystallization mode; for samples heated up and kept at temperatures below 190 degrees C, the crystallization started with thin and long rods or nodules, which grew in the circumferential direction only while their lengths remain unchanged as the time passed. The shape of the nodules can be straight, circular, branched, or entangled, and they can grow parallel to each other or they can be crossed or in a random way. This phenomenon disappeared completely for samples melted and kept at temperatures above 195 degrees C. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2228-2243, 2011