Experiments were conducted to investigate herbicide resistance in wild oat, canary grass, rye grass, and barnyard grass that were collected from Khuzestan, Fars, Markazi, Golestan, Kermanshah, Azarbayjan, Gilan and Mazandaran Provinces during 2004 to 2008. From among 333 collected weed biotypes collected, 319 weed biotypes were suspected to be resistant to and 14 to be susceptible to herbicides. It was found that 182 wild oat biotypes, 61 canary grass biotypes and 14 ryegrasses out of the collected biotypes showed resistance to acetyl-CoA carboxylase inhibiting herbicides (including Clodinafop-propargyl, fenoxaprop P ethyl and Diclofop methyl) and 76 weed biotypes showed suspected resistance or resistance to Propanil, Butachlor, Molinate and Thiobenkarb herbicides. The results indicated that 82 biotypes out of 333 biotypes (26%) collected from 92 fields (525 ha) showed resistance, 99 biotypes (30%) collected from 86 fields (625 ha) were tolerant and 152 biotypes (46%) collected from 68 fields (498 ha) did not show any herbicide resistance. Based on the number of resistant samples, the fields or field area was 298%, 283% and 203% respectively in 2008 as compared to 2005. It is incontrovertible that the number of infested fields to resistant weed biotypes is increasing and serious intensification was reported in the cases of wild oat, canary grass and rye grass, respectively. It was also reported that the maximum frequency, area and the number of infested fields to resistant wild oat was detected in Khuzestan, Kermanshah, Fars, Golestan and Ilam Provinces. The maximum frequency, area and the number of infested fields to resistant canary grass was found in Khuzestan, Golestan and Fars Provinces.