Comparative cross-sectional study among 57 telephonist and 35 clerical staffs was conducted from 2008 to 2009. There was a statistically significant decrease in some EEG indicators before and after their work shifts such as: Alpha wave amplitude from 45,78 + or - 14,10 uV to 39,07 + or - 14,93 uV
Alpha wave index from 47,54 + or - 12,06 percent to 41,83 + or - 9,48 percent. The decrease of telephonist in Hanoi were statistically significant much more than in other provinces. the findings showed a highly fatigue of telephonists during the working time.