Purpose – The purpose of this paper is to improve the productivity of a large-sized frozen chicken manufacturer in Thailand. It analyses the production process based on work study principles and identifies the bottleneck operation. It develops three models for the chicken preparation process. Design/methodology/approach – First, analyse the current production system by collecting the cycle time of all operations in the production process based on work study principles. Then, design the production network and identify the bottleneck operation. After that, three methods – based on line balancing (LB), theory of constraints, and JIT concepts or ECRS (eliminate, combine, rearrange and simplify) – are proposed and implemented in the actual production line. Findings – With the ECRS concept, the authors implement combine by combining two stations into one station, such as handling and weighing, or weighing batter and mixing it with chicken. Then, Simplify is implemented at job E, or transporting chicken using a cart instead of walking. This method can improve the cycle time and reduce the number of employees. It can increase the line efficiency by up to 94.20 per cent, reduce the number of employees by 14 persons, and reduce the labour cost by 356,160 baht/year. Originality/value – Most agro-industry manufacturing processes are labour intensive. Thus, production LB can help increase productivity and reduce costs. The authors found that the case study company designed the production line without aligning it with the production network. A simple improvement can be made by adjusting the sequence of the work. In addition, the current production line was not lean. Implementation of the ECRS concept to improve production can reduce the waiting time and simplify the job.