Due to the low rate of milk consumption in Thai people compared to the world, the Royal Thai government campaigned school milk in 1992 to encourage primary students to drink milk. Hence, the milk plants in Thailand have served milk to schools and other channels for decades. This research studied the production processes of a pasteurized milk manufacturer, which is a small and medium sized milk plant in the central region of Thailand. Our objective was to improve the productivity and efficiency in a line process of a case study. First, we analysed the production process based on work-study principles. The results showed that the current production efficiency was lower than 70%. It implied that there were waiting times, which are considered wasteful and result in high production costs. Next, the bottleneck operation was identified at the packing process, which depended on machine capacity. Then, combinations of work-study, line balancing and continuous improvement concepts were implemented to improve the efficiency. The normal and standard time in the production processes were determined. Then, we proposed three improvement models. The first method was to reduce unnecessary resources; the second was to increase the efficiency; and the third implemented ECRS concepts. Compared to the current line efficiency of 65.51%, the line efficiency of the three methods was increased to 68.97%, 88.33% and 71.56%, respectively. The number of workers reduced in the three methods were six, four and six, respectively. In addition, we compared the total cost reduction from labour and energy cost saving. The result showed that the total cost reduced per year was 570,283 baht, 437,400 baht and 561,600 baht, respectively. In summary, the productivity of workers and machines can be increased by the proposed methods. Then, the company could provide an incentive for workers to improve productivity.