The objectives of this research were 1) study and compare customer loyalty of Isuzu Tang Sia Huat, Nakhon Pathom Company Limited classified by personal factors, 2) study the service quality factors that affect the loyalty of customers who use the service of Isuzu Tang Sia Huat, Nakhon Pathom Company Limited, Head Office Branch (Sa Ka Tiam). The research uses a quantitative research methodology. The sample group was customers who use the service at Isuzu Tang Sia Huat, Nakhon Pathom Company Limited, the head office branch (Sa Ka Tiam), totaling 280 people. The tool used to collect data is a questionnaire. Data were analyzed by percentage, mean, standard deviation, t-test, one-way analysis of variance and a stepwise multiple regression analysis.

The results showed that the comparison of the customer loyalty who use the services of Isuzu Tang Sia Huat, Nakhon Pathom Company Limited, Head Office Branch (Sa Ka Tiam), classified by personal factors found that gender, age, educational level and average monthly income differed with levels of customer loyalty of Isuzu Tang Sia Huat, Nakhon Pathom Company Limited, Head Office Branch (Sa Ka Tiam) was not significantly different. As for the different professions, there is a level of loyalty among the customers who use the services of Isuzu Tang Sia Huat, Nakhon Pathom Company Limited, Head Office Branch (Sa Ka Tiam), differed statistically. As for service quality factors that affect the loyalty of customers who use the services of Isuzu Tang Sia Huat, Nakhon Pathom Company Limited, Head Office Branch (Sa Ka Tiam) found that the response to demand factors; the concrete aspect of the service, service attention and confidence in service, affects the loyalty of customers who use the service.