Internal motivation factors in work achievement, profession advancement, recognition, and likes/dislikes of the job have a relationship with the development of job performance of the production workers’ skills at a basic lubricant production factory in Rayong province. This may be due to the development of performance skills requires multiple internal motivation aspects and may be caused by working seniority, and stable average monthly income that makes them reluctant to develop performance skills to the fullest potential unless they have enough internal motivation.