Compare other countries studies associated with field bindweed (Convolvulus arvensis L.) biological control is too short in Iran. Field bindweed is a major weed of several field crops. During a survey, we focus to finding natural enemies of this weed in Khorasan Razavi province for two years. This paper reports the presence of a seed beetle Spermophagus sericeus Geoffroy as a major natural enemy against field bindweed (Convolvulus arvensis L.) in northeast of Iran. Samples of field bindweeds capsules and seeds collected in tomato fields at two locations in that region. Results showed that the reproductive organs of field bindweed were severely damaged, where 76 and 62 percent of capsules and seeds were infested by S. sericeus respectively. Our findings showed the high level control of field bindweed by S. sericeus and this beetle can be considered as a proper bio control agent for this weed in Iran. However more studies about host specificity of this beetle should be performed.