This study introduces the use of mixed-format multidimensional item response theory (MIRT) analysis for assessing the latent factor structure of the Social Capital Rating Scale (SCRS). The rating scale, an instrument developed for measuring the parent involvement and the peer network of high school students, contains twenty-two items selected from the student questionnaire of the National Educational Longitudinal Study (NELS:88) Database. The psychometric properties and dimensionality of the scale are evaluated with MIRT framework. Using the sample of grade eight students from NELS:88 (N = 27,394), the two-factor structure of the SCRS (factor 1: within-family social capital; factor 2: peer social capital) was confirmed with the two-parameter IRT model (2PL): RMSEA = 0.049, CFI = 0.915, TLI = 0.905, SRMSR = 0.057. Discussion includes methodological implications for social capital scale, focusing on assessment of measurement invariance in differential item functioning etc.