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This study investigated whether differences existed in the measured values between the old and new NaI (Tl) scintillator survey meters (hereafter: survey meter) used to measure the air dose rates in the forests of Fukushima Prefecture. The research was conducted at three sites in Kawauchi village, Fukushima Prefecture (a Japanese cypress forest and a deciduous broad-leaved forest at the Mitsuishi site and a Japanese cedar forest at the Kanayama site), and the air dose rates were measured at heights of 1 m and 10 cm above the ground surface at 50 different points using four survey meters (two new and two old models). The comparisons revealed no significant differences in the air dose rates at heights of 1 m and 10 cm between the same survey meters (for both the old and new models). The results also confirmed that there were no differences in the measured values of the air dose rates between the new and old models. These results indicated that 1) even when two survey meters are simultaneously used to efficiently measure the air dose rates in the forest, the measured values of the air dose rates are unaffected, and 2) updating the survey meter from an old to a new model does not affect the assessment of the interannual variability in the air dose rates.