TO SURVEY THE CROSS RESISTANCE TO ACETYL-COA CARBOXYLASE (ACCASE) INHIBITOR HERBICIDES IN WILD OAT (AVENA LUDOVICIANA) POPULATIONS COLLECTED FROM MARVDASHT FIELDS, SEEDLING BIOASSAY EXPERIMENTS WERE CONDUCTED ON FIVE WILD OAT POPULATIONS (4 SUSPECT POPULATIONS TO RESISTANCE AND ONE SUSCEPTIBLE POPULATION TO HERBICIDE) AT THE DEPARTMENT OF WEED RESEARCH, PLANT PROTECTION INSTITUTE GREENHOUSE IN 2008-2009. IN THESE EXPERIMENTS, WILD OAT POPULATIONS WERE SPRAYED DURING 2-4 LEAVES STAGE USING THE EIGHT DOSES (0 TO 16 TIMES OF RECOMMENDED DOSE) OF CLODINAFOP PROPARGYL, SETHOXYDIM AND PINOXADEN HERBICIDES. SHOOT BIOMASS WERE PERFORMED FOUR WEEKS AFTER HERBICIDES APPLICATION. IN ORDER TO OBTAIN THE RESISTANCE INDEX, GR50 OF SUSCEPTIBLE POPULATION WAS DETERMINATE AND THEN RESPONSE OF ALL POPULATION WAS EVALUATED RELATED TO THAT. RESULTS OF THESE STUDIES INDICATED THAT M1, M2, M3 AND M4 POPULATIONS WERE CROSS RESISTANT TO CLODINAFOP PROPARGYL AND SETHOXYDIM HERBICIDES WITH DIFFERENT DEGREES. ALSO, M1 AND M3 POPULATIONS INDICATED CROSS RESISTANCE TO PER THREE HERBICIDES. FURTHERMORE M2 AND M4 POPULATIONS WERE MORE SENSITIVE THAN SUSCEPTIBLE POPULATION TO CLODINAFOP PROPARGYL HERBICIDE.