A maintenance optimization model is developed to maximize the net value of imperfect degradation-based maintenance by determining an optimal interval of condition monitoring and the degradation level after imperfect repairs. The proposed decision model intends to maximize the difference between the maintenance value and the expected total cost of maintenance during a life cycle. The value of maintenance depends on the expected life cycle length which positively affected by maintenance activities. The value-based strategy advocates applying more frequent monitoring. However, the optimal net value might be insensitive to the degradation level after repair. It implies the possibility of reaching the maximum value of maintenance even without the highest level of repairs.