Freezing and aging under frozen conditions could be a potential technique for modifying characteristics of aggregated sodium caseinate particles. In this research, 1% sodium caseinate suspensions with different NaCl concentrations (0.1 M and 0.01 M) and pH (5.5 and 8.0) were frozen at −35 °C for 1 h, 2 days, or 5 days. After thawing, the suspensions were analyzed by a tunable resistive pulse sensing device. Particle diameter was significantly larger in suspensions with 0.1 M NaCl than suspensions with 0.01 M NaCl. Particle diameter of the samples decreased during the 1st hour of freezing, then gradually increased up to the 2nd and 5th day of the freezing process. In contrast, particle number concentration of most samples increased after 1 h of freezing and decreased up to the 2nd and 5th day of the freezing process. After being frozen, surface characteristics of the casein aggregates changed, most notably in the solution with pH 5.5 and NaCl concentration of 0.01 M. It was found that different aging temperatures (−5, −20, and −35 °C) had similar effects on particle diameter and particle number concentration, but had different effects on the change in surface characteristics. Based on these results, characteristics of different sodium caseinate suspensions could be strategically modified by using freezing and aging technique.