BACKGROUND: Working at height has always been considered as one of the most dangerous industrial activities. Workers' fitness including their physical and psychological ability plays a key role in prevention of occupational accidents. This research was conducted to investigate the physical and mental fitness of telecommunication tower climbers as well as their job stress. METHODS: This cross-sectional study was conducted among employees of a contracting company which worked in the field of telecommunication tower installation in Iran during 2016. Sixty out of 93 workers voluntarily participated in this study. Data collection tools were the Persian version of the Work Ability Index (WAI), the Persian version of the Health and Safety Executive (HSE) Stress Indicator Tool and an author-developed measure to assess socio-demographic characteristics. Data was analyzed through statistical tests such as independent t-test, univariate analyses of variance (ANOVAs), Pearson's correlation coefficient, and multivariate linear regression; using SPSS 19 software. RESULTS: Workers' mean ± SD WAI score was 29.17 ± 10.33 and for work-related stress was 3.08 ± 1.80. There was a significant relation between WAI and educational level, job tenure, hours of sleep per day, regular exercise, and second job. The repression modeling explained 67.4% of the total variance (adjusted R2) of the WAI score. Among the dimensions of work related stress, control (β= 0.21) and changes (β= -0. 40) were significant predictors of the WAI score. CONCLUSIONS: To improve the worker's work ability, intervention programs should focus on promoting level of job control, sleep quality and exercise. Additionally, implementing a comprehensive macroergonomics and participatory program for increase involvement the workers in organization changes should be considered.