Modified Kelly-Pettenkofer (MKP) medium is one of the several media used for isolation and cultivation of Borrelia. The aim of the study was to assess whether particular Borrelia species (B. afzelii, B. garinii, and B. burgdorferi sensu stricto) have the ability to grow in MKP medium stored at +4 °C for periods for 1 month up to 1 year, and how prolonged storage may influences Borrelia growth and morphology. The growth of Borrelia was evaluated after 5 days of incubation at 33 °C: cell count per mL, morphology, and motility were assessed. The results of this study showed that the duration of storage of MKP medium had statistically significant influence on growth of B. afzelii (p = 0.021) and B. garinii (p = 0.004), but not on growth of B. burgdorferi sensu stricto (p = 0.204), whereas duration of storage of the medium had no impact on Borrelia morphology and motility. The results of the study indicate that medium stored for more than 1 and up to 12 months supports Borrelia growth.