Out-of-hospital cardiac arrest (OHCA) is a serious condition. The volume-outcome relationship and various post-cardiac arrest care elements are believed to be associated with improved neurological outcomes. Although previous studies have investigated the volume-outcome relationship, adjusting for post-cardiac arrest care, intra-class correlation for each institution, and other covariates may have been insufficient. To investigate the volume-outcome relationships and favorable neurological outcomes among OHCA cases in each institution. We conducted a prospective observational study of adult patients with non-traumatic OHCA using the OHCA registry in Japan. The primary outcome was 30-day favorable neurological outcomes, and the secondary outcome was 30-day survival. We set the cutoff values to trisect the number of patients as equally as possible and classified institutions into high-, middle-, and low-volume. Generalized estimating equations (GEE) were performed to adjust for covariates and within-hospital clustering. Among the 9909 registry patients, 7857 were included. These patients were transported to either low- (2679), middle- (2657), or high- (2521) volume institutions. The median number of eligible patients per institution in 19 months of study periods was 82 (range, 1-207), 252 (range, 210-353), and 463 (range, 390-701), respectively. After multivariable GEE using the low-volume institution as a reference, no significant difference in odds ratios and 95% confidence intervals were noted for 30-day favorable neurological outcomes for middle volume 1.22 (0.69-2.17) and high volume 0.80 (0.47-1.37) institutions. Moreover, there was no significant difference for 30-day survival for middle volume 1.02 (0.51-2.02) and high volume 1.09 (0.53-2.23) institutions. The patient volume of each institution was not associated with 30-day favorable neurological outcomes. Although this result needs to be evaluated more comprehensively, there may be no need to set strict requirements for the type of institution when selecting a destination for OHCA cases.