Abstract: An automated system for controlling the curing process of structures formed of fiber-reinforced composite material and the like in an autoclave is disclosed. The system uses sensors to monitor autoclave pressure, ambient and structure surface temperature, and structure viscosity during the cure cycle. Real time measurements are taken for each of these parameters, and the measured values are compared with predetermined optimum values which themselves change as the curing cycle progresses. The results of the comparisons are used to control the application of temperature and pressure in the autoclave to achieve the desired visco-elastic states of the structure which continually change as the curing process progresses. The viscosity data are obtained through measurements of attenuation of an ultrasonic wave in the composite material of the structure. It was found that the attenuation is directly related to the viscosity of the structure.