This study aimed to verify the construct validity of "Comfort Items in Critical Care" developed to clarify the comfort of critically ill patients. Methods: Data were collected through an online questionnaire between February and March of 2020 and analyzed with a confirmatory factor analysis. Participants were 120 certified nurse specialists in critical care nursing, certified nurses in intensive care, and certified nurses in emergency nursing, from Japan. "Comfort Items in Critical Care" comprises 34 items and is designed to measure 6 categories of comfort: "relief of symptoms", "independence", "calmness", "satisfaction", "stable physiological responses", and "calm behavior and asleep", Participants rated the appropriateness of each item using a 4-point Likert scale. Results: The "Comfort Items in Critical Care" scores ranged from a mean of 3.10 to 3.93. Item-total correlation coefficients ranged from ρ = .300 to .636. The standardized path coefficient for "being able to endure" (β = .15, p = .103) was eliminated because it was not significant. Confirmatory factor analysis supported a two-factor structure "comfort measured by patient subjectivity" and "comfort measured by nurse observation". That model fit met the reference values the path coefficient between the latent variables of .61. Conclusion: This study confirmed the construct validity of comfort in critical care nursing based on nursesʼ perceptions. The emphasis was on "calmness", "satisfaction", and "calm behavior and asleep". Each item in "Comfort Items in Critical Care" is an assessment perspective for providing comfort care to critically ill patients.