Background: The World Health Organization (WHO) states that no safe level of lead exposure has been established and compared with adults, children absorb approximately four to five times more lead into their bodies. When blood lead levels reach 3.5 µg/dL, which may lead to decreased intellectual capacity, impaired attention, and learning difficulties, potentially resulting in intellectual disability and behavioral disorders. The nervous system and blood–brain barrier in children and adolescents are not fully developed, making them highly susceptible to the neurotoxic effects of lead. Lead disrupts several neurotransmitter systems, including dopaminergic, glutamatergic, and cholinergic pathways. Dysfunction in these systems—particularly alterations in dopaminergic pathways—is closely associated with symptoms of Attention Deficit Hyperactivity Disorder (ADHD). In Mongolia, previous studies have investigated the association between ADHD and lead levels in hair samples among children; however, no studies have examined the relationship between blood lead levels and ADHD. Determining whether blood lead levels influence ADHD in children will provide a scientific basis for preventive measures and the development of additional treatment strategies to reduce clinical symptoms and support clinical practice. Aim: To investigate the association between blood lead levels and ADHD among school children. Materials and Methods: A household-based analytical cross-sectional study was conducted. A total of 306 children aged 6-14 years were randomly selected according to the study inclusion criteria. The Vanderbilt ADHD Diagnostic Questionnaire was administered to parents/guardians and classroom teachers to identify ADHD cases. Blood samples were analyzed to determine blood lead levels using the NIOSH 8005 standard method with Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) in a laboratory accredited under MNS ISO 17025:2018. Additionally, data on lead exposure risk factors were collected using a 15-item questionnaire administered to parents or guardians through the Google Forms platform. Result: Among the participants, 34 children were diagnosed with ADHD. Of these cases, 67.64% were male and 32.35% were female, yielding a male-to-female ratio of approximately 2:1. Boys were 3.6 times more likely to have ADHD than girls (OR=3.675; 95% CI: 2.276-6.210; p<0.0001). Regarding ADHD subtypes, the predominantly inattentive type accounted for 38.2% (n=13), the predominantly hyperactive type for 52.9% (n=18), and the combined type for 8.8% (n=3). When comparing clinical subtypes by sex, the hyperactive type was more common among boys (60.9%, n=14), whereas the inattentive type was more common among girls (45.5%, n=5). The mean blood lead level among all children was 4.8±2.33 µg/dL. Among children with ADHD, the mean level was 6.16±2.47 µg/dL, while among children without ADHD it was 4.75±2.31 µg/dL, indicating a statistically significant difference between the groups. In examining factors influencing the development of ADHD in relation to children’s morbidity status, repeated illnesses such as anemia, rickets, malnutrition, and recurrent acute febrile diseases were identified as statistically significant risk factors (p=0.012). In contrast, acute conditions of short duration were not found to be significant risk factors. Conclusion 1. Among the children included in the study, 34 (11.1%) were diagnosed with ADHD, and the prevalence was higher in boys than in girls. 2. Blood lead levels showed a statistically significant association with Attention Deficit Hyperactivity Disorder in children.