A number of studies attest to the effectiveness of virtual patients in fostering and assessing students' development of clinical reasoning. An objective assessment of students' clinical reasoning is, however, challenging. This study focused on determining the psychometric properties of the virtual patient version of the Lasater Clinical Judgment Rubric, a rubric that is aimed at assessing nursing students' clinical reasoning processes when encountering virtual patients. A nonexperimental design was used in which data from 125 students' reflections on solving two different virtual patient scenarios were included in the analysis. First, a deductive content analysis was conducted using the categories of the rubric as a lens. After that, each student's performance was quantified according to the different levels of the rubric. Exploratory factor analysis and test of normality and reliability, including the Kaiser-Meyer-Olkin test, Bartlett's test, the Shapiro-Wilk test, and Cronbach's alpha were used in the analysis. The result suggested three factors: "Understanding the patient", "Care planning" and "Reflecting" that explained 81.8% of the variance. Cronbach's alpha was 0.931. The result showed the rubric to be a valid assessment instrument for assessing nursing students' clinical reasoning when encountering virtual patients.