Twenty-four purified rice blast isolates of Pyricularia grisea were isolated at Rice Pathology lab., RRTC, Sakha Kafr El-Seikh Egypt; thirteen from different rice cultivars, and eleven from different weeds. Those isolates were identified to physiological races using the eight international differential varieties under greenhouse conditions. For rice blast isolates, the results show that the isolates are categorized in six race-groups, i.e. five isolates for race group IA, three from group IB, two isolates from ID  race group and one isolate conformed each of  IC, IG and II race groups. The isolates obtained from weeds  were eight isolates conformed of IG race group  and three isolates from ID race groups. A total of 24 rice blast isolates were analysed for their morphological,  geographical and molecular diversity. Two Intron Splice Junction (ISJ ) and 9 Sequence Tagged Microsatellite (STMS) markers wer used for the molecular diversity assessment of the tested rice blast isolates. Their was a noticable colenearity detected between haplotype and pathotype with few exceptions noticed. All rice specific markers used were successfully amplified with the fungus isolates, indicating a sufficent level of similarity between the rice and the blast fungus in these genetic loci. All weed isolated were clusterd in the middele of the dendrogram except one agressive isolate which clustered with another rice agressive isolate, the later one is the isolate broke down the resistance of the leading variety Sakha 101. These results demonstrate the usfelness of molecular diversity in assessment and differentiation of pathogenicity and host specificity among the blast fungus isolats. One dworback of the current investigation is the low number of molecular markers used and this may in partial explains the few exceptions recorded.