Background of study: Using nitrous oxide for sedation in paediatric dentistry is effective. Pollution from nitous oxide traces is an occupational hazard which should be monitored. Aim / Objective: to compare the nitrous oxide traces between different dental procedures and to monitor the nitrous oxide traces in the working environment. Research Methodology: Nitrous oxide was measured in 27 dental procedures according to two methods. First method, measurements were recorded every two minutes during the inhalational sessions. Second method measurements were recorded from different distances from the operation site. Results: Twenty one sessions used for the first method. No statistical difference was found between the means of the nitrous oxide traces through the extraction and conservative sessions. Age group from 6 to 8 years had the highest measured traces. High traces recorded during stressful events. Six sessions were selected for the second method. The distance obeys the inverse square law. Conclusion: lack of cooperation would lead to excessive pollution. Encouraging patient to breathe through the nose was found be very helpful in reducing pollution. It is recommended to check the equipment for leaks, to make sure that the mask is of the appropriate size and tight fitting, and to ensure that scavenging and surgery ventilation is adequate.