This paper proposes a joint inspection-based main-tenance and spare ordering optimization policy that considers the problem of integrated inspection, preventive maintenance, spare ordering, and quality control for a four-state single-unit manufacturing system. When an inspection detects a minor de-fect, a second phase inspection is initiated and a regular order is placed. Product quality begins to deteriorate when the system undergoes a severe defect. To counter this, an advanced re-placement of the minor defective system is carried out at the Jth second phase inspection. If a severe defect is recognized prior to the Jth inspection, or if system failure occurs, preventive orcorrective replacement is executed. The timeliness of replace-ment depends on the availability of spare. We adopt two modes of ordering: a regular order and an emergency order. Meanwhile, a threshold level is introduced to determine whether an emer-gency order is preferred even when the regular order is already ordered but has not yet arrived. The optimal joint inspection-based maintenance and spare ordering policy is formulated by minimizing the expected cost per unit time. A simulation al-gorithm is proposed to obtain the optimal two-phase inspection interval, threshold level and advanced replacement interval. Re-sults from several numerical examples demonstrate that, in terms of the expected cost per unit time, our proposed model is superior to some existing models.