Background and aims:Work-related musculoskeletal disorders (WMSDS) is one of the mostimportant problems in working populations of Iranian industries; so, in order to evaluate theintegrated roles and effects of various ergonomic risk factors inducing such disorders, the StrainIndex (SI) methods was used.Methods: This was a cross-sectional study conducted on 448 male subjects including 63controls working in administrative jobs and 385 cases working in lathing, welding, melting andfoundry jobs using integrated procedure which includes observations, interview, NordicMusculoskeletal Questionnaire (NMQ) methods and SI model. All workers were questioned.Data were analyzed using SPSS software v. 11 and Excel package.Results: The most prevalent MSDs in upper limbs were found in melting lathing, foundry andwelding respectively. There was a significant relationship between age and job groups (c2=7.33;df=16; p<0.001). One-way analysis of variance showed a significant differences among means ofcalculated Strain Indices of administrative (1.06), lathing (6.52), welding (3.68), melting (7.79)and foundry (6.33) jobs (F=5.92; df=16; p=0.005). Also it was revealed that melting job wasattributed as "hazardous job" (4 risk level), lathing and foundry jobs were referred to "moderaterisk level" (3 risk level), welding job was allocated as "uncertain risk level" (2 risk level), andadministrative job was attributed as "safe risk level" (1 risk level). Moreover, there was asignificant relationship between DUE and job groups (c2=11.92; df=12; p=0.004).The paired ttestshowed significant difference with direct and relatively complete correlation between meansof Strain Indices in right (6.53) and left (4.29) hands (r=0.69; t=3.15; p<0.001).Conclusion: The Strain Index (SI) model can be referred as an efficient and applicable methodfor the assessment of ergonomics risk factors inducing upper extremity musculoskeletal disorders(UEMSDs), classifying jobs, correcting and modifying work situations and preventing DUEmusculoskeletal disorders.