To investigate whether the application of manual pressure to the injection site before intramuscular injection reduces pain. An experimental study with intrasubject comparison was conducted using manual pressure to reduce pain associated with intramuscular injection. Seventy-four subjects, participating in an immunization vaccination campaign, were recruited by convenience sampling from a university. They were required to receive two doses of vaccines via intramuscular injections. One was given in a conventional way, i.e. without manual pressure being applied prior to the injection (control condition). The other was given with manual pressure being applied prior to the injection (experimental condition) for 10 seconds. The two conditions were randomly allocated for each subject. The instrument for measuring the perceived pain intensity was the Pain Intensity Verbal Rating Scale (Cantonese). To ensure the consistency of manual pressure being applied to the injection site, a mechanical pressure sensor device was used to record the manual pressure being applied. The mean manual pressure applied was 190.82 mmHg (SD=5.25). Results demonstrated a significant difference in the perceived pain intensity for experimental and control conditions. Subjects with manual pressure applied before injections reported lower pain intensity scores, whilst those without the application of manual pressure before injections reported higher pain intensity scores. Applying manual pressure to an injection site before performing an injection could be an effective means of decreasing pain intensity.