Manual load lifting is the most common and stressful activity that imposes high biomechanical pressures on the body, particularly on the back. Diverse studies have shown that load lifting can cause work-related musculoskeletal disorders among workers. This study was conducted to assess manual lifting activity using NIOSH equation and WISHA index and compare the results of the two methods in workers with manual lifting activities. This cross- sectional study was carried out among 120 workers with manual lifting activity in 7 industrial settings of Shiraz city. Nordic Musculoskeletal disorders Questionnaire (NMQ) and demographic questionnaire, as well as NIOSH lifting equation and WISHA index were used to gather the required data. Statistical analyses were performed using SPSS, 19. The results showed that back problems were the most frequent musculoskeletal disorders among the workers studied (68.3%). The results of lifting evaluation indicated that 79.2% of the individuals in the NIOSH method and 39.2% in WISHA index were at risk of back injuries. The kappa value was equal to 0.29, indicating a fair agreement between the results of assessment by the two methods. The results of this study confirmed a fair correlation between these two assessment methods, so they might be used interchangeably.