Hydrogen and deuterium trapping sites in high-strength steels have been observed by secondary ion mass spectrometry (SIMS). High-strength steels with 1400 MPa tensile strength are loaded and dipped in D₂O and 20% NH₄SCN solution at 323 K to occlude hydrogen and deuterium. As a result, the depth profiles by SIMS show the presence of deuterium means hydrogen trapping site occluded during delayed fracture test. Secondary ion-image analysis by SIMS has made possible to observe hydrogen and deuterium trapping sites in high-strength steels. Hydrogen tends to accumulate at grain boundaries, in segregation bands, and in inclusions. Line scans by SIMS show that the concentration of hydrogen is 7.8 times as high at grain boundaries as in the matrix, 5.0 times as high in the segregation bands, and 11 times as high in the inclusions. Hydrogen trapping sites at grain boundaries can be observed by measuring after the delayed fracture test as soon as possible.