Introduction: Job back pain is one of the most common occupational diseases and injuries in the world that affects people's physical and mental health. The purpose of this study was to evaluate the BCF using the UTAH method in manual handling tasks among workers of a chemical manufacturing company. Methods: This descriptive and cross-sectional study was carried out on 35 people who had manual handling tasks and worked in a chemical factory in April and May 2018. The participants were selected using the simple random sampling method. In this study, UTAH method and standard Cornell questionnaire were used to collect the data. Finally, we run descriptive statistics and ANOVA test to analyze the data using the SPSS19. Results: The average amount of BCF calculated using the UTAH method showed that the load pressure on back for the jobs of repair unit (400 kg), discharge and loading unit (460 kg), and warehouse unit (370 kg) exceeded the standard. Moreover, the results of the Cornell questionnaire indicated that 68 percent (N = 24) of individuals in the mentioned occupations were suffering from lower back pain. Conclusion: The findings of this study showed that the UTAH method is useful for estimating the BCF in manual handling tasks. We also found that 68 percent of the participants had occupational back pain. So, interventions should be conducted and measures should be taken to reduce these disorders.