OBJECTIVE: The aim of this study was to investigate the association between plasma glucose (PG), HbA1c and plasma glucagons levels in children with type 1 diabetes to determine the influence of plasma glucagon on their glycemic control. METHODS: The study was conducted in 60 Japanese children, aged 13.3 ± 4.6 years, with type 1 diabetes for at least 3 years of diabetes. Most of the subjects had absent pancreatic β-cell function. We compared the glucagon levels among patient groups stratified according to the 2-hour postprandial levels (<50, 50-99, 100-199, 200-299, and ≥ 300 mg/dL), and the HbA1c levels (<7.0, 7.0-7.9, 8.0-8.9, and ≥ 9%). RESULTS: The mean 2-hour postprandial PG, HbA1c and plasma glucagon levels were 174 ± 97 mg/dL, 7.7 ± 1.3% and 84.0 ± 32.6 pg/mL, respectively. The glucagon levels were highly correlated with the PG levels (r=0.553, P<0.0001) and mildly correlated with the HbA1c levels (r=0.301, P=0.0192). Patients with high PG levels had significantly higher levels of glucagon as compared with those with lower PG levels (139.4 ± 47.2, 78.4 ± 17.3, 82.4 ± 21.0, 98.3 ± 29.2 and 93.8 ± 18.3 pg/mL, P=0.0009). On the other hand, there were no significant differences in plasma glucagon levels among patient groups stratified according to HbA1c levels (P=0.1566), however, patients with HbA1c levels ≥ 9% had significantly higher levels of glucagon than those with HbA1c levels < 7% (113.3 ± 53.4 vs 80.8 ± 18.4 pg/mL, P=0.0291). CONCLUSION: These results suggest that patients with high PG are likely to have high concentrations of plasma glucagon, which may aggravate glycemic control progressively, leading to elevation of HbA1c levels.