Multi-Plant Ready-Mixed Concrete Industry is currently one of the most famous industry. It is obvious that the competition is very high. Services become the best marketing approach. To keep Ready-Mixed concrete machines in good condition and ready to operate at all time, an effective maintenance plan must be developed and executed. The objective of this study was to developed the effective maintenance plan in order to reduce machine downtime. Breakdown maintenance was a major activity to upkeep the machines in the factory. The management relied heavily on skills and experiences of workers in repairing and maintaining the machines. Records of machine downtime per month and machine downtime index were collected for the period of 3 months. The proposed maintenance plan consisted of a 5-year maintenance plan, an annual maintenance plan and a weekly maintenance plan. The plan included a maintenance organization providing each personnel a job description with full responsibility and accountability. Documentation and parts supporting systems were also described. The plan had been implemented in real work situation for 6 months. The downtime per month and downtime index were then recorded and compared with the previous records. It was found out that downtimes per month of ELBA 1 cubicmeter, ELBA 1/2 cubicmeter, KABAG 1 cubicmeter and KABAG 1/2 cubicmeter were reduced by 216,444,369 and 807 minutes, respectively. The machine downtime indices of above machines were reduced by 1.47%, 7.85%, 11.86% and 7.89%, respectively.