Abstract Objective To investigate the effects of combination therapy with cholecalciferol and lansoprazole on residual β-cell function and glycemic control in children with new-onset type 1 diabetes. Methods Children aged 6-12 years with type 1 diabetes were allocated to receive cholecalciferol and lansoprazole (Group 1) or no treatment (Group 2). Children were maintained on their respective insulin regimens and kept records of blood sugar and insulin doses taken. Children were followed at three-month intervals for six months. Changes in mean fasting C-peptide and HbA1c levels, daily insulin doses, fasting blood glucose and mean blood glucose levels from baseline to end of the study were analyzed. Results Twenty-eight children (14 per group) met the eligibility criteria. Fasting C-peptide levels decreased significantly from baseline to study end in both groups (mean decrease -0.19±0.09ng/mL and -0.28±0.08ng/mL, p=0.04 and p=0.001; Group 1 and Group 2 respectively). However, fasting C-peptide level drop was significantly smaller in Group 1 compared to Group 2 (30.6% and 47.5% respectively; p=0.001). Likewise, daily insulin doses decreased significantly in both groups (-0.59±0.14units/kg and -0.37±0.24units/kg respectively; p=0.001). All patients recruited completed the study. No adverse events were reported. Conclusion Combined therapy with cholecalciferol and lansoprazole for six months was associated with smaller decline in residual β-cell function and lower insulin requirements in children with new-onset type 1 diabetes. Preliminary findings of this small-scale study need to be confirmed by larger studies. Registry of Clinical Trials (www.ctri.nic.in) under number REF/2021/03/041415 N.