Thalassaemia and abnormal haemoglobins are the most common genetic disorder worldwide. School-based screening thalassaemia program for form four students was introduced with the objective to screen for the thalassaemia status. There is paucity in the data in Kedah on distribution of thalassaemia carrier and the associated factors. Hence this study aims to identify the factors associated with being a thalassaemia carrier and to describe the laboratory cost for the thalassaemia screening. This study used secondary data from the school-based thalassaemia screening in 2018 obtained from Kedah State Health Department. Results showed the prevalence of thalassaemia carrier among form four students in Kedah was 10.91%. Multivariate logistic regression showed that students from Baling, Padang Terap and Yan were 1.40, 1.34 and 1.23 times more likely to be a thalassaemia carrier respectively compared to Kota Setar (aOR Baling 1.40;95% CI 1.21,1.64; aOR Padang Terap 1.34;95% CI 1.11,1.61 and aOR Yan 1.23;95% CI 1.03,1.47). Malay and Siamese students were five times more likely be thalassaemia carriers compared to Indian (aOR Malay 5.16;95%CI 3.42,7.79, aOR Siamese 5.63;95%CI 3.19,9.97). Meanwhile, Chinese students had 2.61 higher odds to be a thalassaemia carrier compared to Indian (aOR Chinese 2.61;95%CI 1.65,4.12). The laboratory cost for the thalassaemia screening ranged from RM2.14 to RM142.14 per participant. As for conclusion, this study reported high prevalence (10.91%) of thalassaemia carriers in Kedah. Our study also confirmed that the district and the ethnicity significantly influenced the thalassaemia carrier status. The identified factors should inform future thalassaemia campaign to prevent higher prevalence of thalassaemia patients.