Firefighting is arduous work and it requires a high level of physical fitness and readiness. The purpose of this study is to assess the physical fitness and readiness levels of the Turkish firefighters and investigate the effects of 12-week exercise on firefighters' fitness levels. The study was an experimental study in which 41 firefighters were participated voluntarily. Ethics committee approval and written consents were obtained prior to the study. The experiment group attended to a 12-week planned exercise sessions for two times per week for 90 min. The control group did not participate into a planned exercise during that period. Any caloric restrictions were not recommended nor were calorie intakes controlled in either group. As the Shapiro-Wilk and Q-Q plot tests revealed that the data were normally distributed, independent samples t-test, paired-samples t-test, and Pearson's r to analyse data. The results indicated that body mass index levels of the firefighters in both groups were over the critical level suggested by the World Health Organization and their VO[subscript 2]max levels did not meet the minimum requirements. It was also found that BMI had disruptive effects on physical performance. The experimental group had significant improvement after attendance to 12-week training but the control group's performances were worsened. It was concluded that the firefighters' physical performances were low and they were highly prone to be obese. Instant measures, including promoting exercise and regularly testing the physical performance levels of the personnel, should be taken to reverse the current undesirable situation.