Background: This study aims to evaluate the inter-rater reliability and perceived usability of a newly developed drug-related problem (DRP) classification system for use by pharmacists in the intermediate and long-term care (ILTC) setting in Singapore. Methods: This was a cross-sectional survey study involving the use of a self-administered questionnaire. All 55 pharmacists affiliated to the Pharmaceutical Society of Singapore (PSS) ILTC Pharmacists Workgroup who were above 21 years old and not authors of the classification system were invited to participate. The inter-rater reliability of participants’ classification of 46 mock DRP cases using the new DRP classification system was determined using Fleiss’s kappa (κ). Participants’ perceived usability of the classification system was evaluated using six items with five-point Likert scales (1—“strongly disagree”, 5—“strongly agree”). Results: Thirty-three pharmacists responded to the survey. Overall inter-rater reliability was found to be substantial (κ = 0.614; 95% CI: 0.611–0.617). All usability items received positive ratings (“strongly agree” or “agree”) from at least 69% of participants. Conclusion: The new DRP classification system has substantial external validity and appears to be suitable for use by pharmacists to document and report DRPs in the ILTC setting in Singapore and facilitate evaluation of the impact of pharmaceutical care in the ILTC setting.