The present paper deals with using a useful method to monitor the wear of the teeth of milled tooth bits during drilling. This approach is done by using two dimensionless parameters TD (dimensionless torque) and RD (dimensionless rate of penetration) . By plotting TD vs. RD , The constants a1 and a2 could be determined and both used to calculate the two other dimensionless parameters ED (bit efficiency) and FD (bit dullness) as a bit dullness evaluation indicators , which could be used rather than other traditional techniques. This approach applied on three wells , Zubair #166 , Zubair #162 and Zubair #174 in Zubair field Southern Iraq .The obtained results could be useful to detect bit wear and according to that, the decision of pulling and using new bits could be determined easily and therefore drilling operations will be actively done with lowest costs and efforts. .