Late posttraumatic epilepsy (PTE) following traumatic brain injury (TBI) is characterized by long and unexpected latencies until the onset of seizure. Interventions with antiepileptic drugs before seizure onset have not been found to prevent late-onset PTE. Greater understanding of the development of epileptogenicity underlying late PTE following TBI is needed to develop effective interventions at an appropriate time-point. Here we describe a simple behavioral evaluation method for detecting each stage in the development of epileptogenicity during the period from TBI until epileptic seizure occurrence in mice. Pilocarpine (250 mg/kg) was injected at different post-operative days into mice subjected to controlled cortical impact (CCI), a common model for experimental TBI. The seizure sensitivity test was then performed. Seizure severity and incidence at the pilocarpine sub-threshold dose gradually increased from 7 days after CCI, reaching a significant increase at 28 days after CCI. The proposed simple pilocarpine test in CCI mice is relevant for monitoring the development of epileptogenicity, and could help researchers develop methods for early diagnosis, prevention and treatment of PTE.