A method of producing a nonaqueous secondary battery includes: preparing an electrode body (S10); constructing a battery assembly with the electrode body and a nonaqueous electrolyte (S20); initially charging the battery assembly (S30); aging the battery assembly at 40° C. or higher (S40); adjusting an SOC of the battery assembly (S60), wherein, the adjusting the SOC is performed such that a residual capacity percentage of the battery assembly is 11.5% or more and 14% or less; self-discharging the battery assembly and measuring a voltage drop amount (S70); and determining a quality of the battery assembly based on the voltage drop amount (S80).