This study aims to study carbon monoxide (CO) concentration in the Federal Territory of Kuala Lumpur (FTKL), which involves primary data through field studies with a quantitative approach. The CO sampling method involves 12 observation stations covering six main zones for eight days. Data are collected twice a day at night and day between 01:00 - 04:00 AM and 1:00 - 4:00 PM. The duration of the sampling is 30 minutes for one sample. Sampling time may vary for stations but still within the stipulated time. The instrument to measure CO is the Model Carbon Monoxide meter AS700A. The Analysis is descriptive. The findings show that the lowest value at night is stations 3 and 10, with an average concentration value of 5 parts per million (ppm). Simultaneously, the highest CO value in the afternoon is at station 1 and station 4, with a concentration of 12 ppm. The overall average at each station is high, between 7 to 12 ppm. Most stations show readings exceeding the WHO's standard (5 ppm/hour). However, CO's concentration is considerably under control because it does not exceed the standard limits of NAAQS and DOE. Overall, CO concentrations are higher in the day than in the morning and on weekdays than on weekends. In conclusion, vehicle increase significantly contributes to increased CO concentrations in Kuala Lumpur. The proactive and effective measures to reduce the well-being of life to maintain human health and the environment.