Salmon milt peptide (SMP), an unused fish processing byproduct, exhibits strong inhibitory activity against dipeptidyl peptidase-IV (DPP-IV) and a suppressive effect on postprandial hyperglycaemia in Sprague-Dawley rats. Herein, we conducted a randomised, placebo-controlled, double-blind, crossover study of healthy Japanese subjects to investigate the effect of glucose loading on postprandial blood glucose levels after one week of administering continuous or single dose of 500 mg of SMP. The primary and secondary outcomes of reduced blood glucose and insulin levels were not met in the 14 subjects included in the analysis. This may be due to the ineffectiveness of SMP in insulin resistance due to its DPP-IV inhibitory activity. Therefore, we conducted a SMP subgroup analysis based on the homeostasis model assessment of insulin resistance (HOMA-IR); the group with normal HOMA-IR (<1.6) had a significantly lower area under the curve and blood glucose at 60 min after glucose loading than the group with HOMA-IR ≥1.6. These results suggest that SMP is effective in subjects without insulin resistance. There were no adverse events associated with the test food, and SMP was considered safe. This report is the first to investigate the effect of a food ingredient with DPP-IV inhibitory activity in a clinical trial.