Background & Objectives: Motor vehicle traffic in streets is one of the main causes of noise pollution in the environment. Present study aimed to determine day average sound level Index in overcrowded areas of Birjand, Iran. Methods: Noise level in selected stations was measured by TES sound level meter using BS 7445-1-2003 and BS 7445-3-1991 standards. The measurement was done on working days and weekends according to the enactment of the Council for Environment of Iran. Data were processed using SPSS software. Results: The average day noise level was 66.7 ± 2.2 dB with the highest level belonging to Motahari St. (69.1 dB). Mean noise level on working days was 67.8 ± 2.3 dB and on weekends was 65.1 ± 2.2 dB that are higher than the standard limit (p<0.05). Conclusion: Regarding the harmful effects of this environmental agent, more studies are recommended to investigate causes of the noise pollution. Since traffic load are the main determinant of the noise pollution passing traffic rules and educating residents to promote culture of motor vehicle driving may decrease noise pollution level and prevent its physical and mental disorders in such areas.