The present study was an attempt to investigate service quality assessment within notable chain restaurants of Tehran. More specifically, the study aimed at conducting a research on two famous, active and successful chain restaurants of Tehran in comparative mode to see how well their service qualities are and if the service quality they offer has any deficiencies. They wereselected for the present study based on their fame and background. One of these two was a traditional food restaurant, namely Hani, and the other one was Boof restaurant which provides fast food. To do the study, Service Quality Scale (Caruana, 2002) was employed to measure the service quality of the restaurants aforementioned. 120 questionnaires were distributed and seventy completed ones were returned. The customers’ presented data was used to find out the significant factors considered in the evaluation of service quality in Haani and Boof restaurants, satisfaction and loyalty degree of customers in these two restaurants.The data collected were analyzed via employing SPSS software version 21, employing descriptive statistics, t-test, andmultivariate ANOVA (MANOVA). Based on the results it was revealed that among theservice quality factors on time servicing, accountability, and staff interaction were the mostsignificant ones for the customers while decoration and face validity was the least significant factor. It was also found that there was not any significant difference between Boof and Haani’s costumer satisfactions, but in terms of loyalty factors the way the restaurant was introduced, rate of keeping costumers and evaluation, Boof restaurant’s costumers significantly trusted the persons who introduced it more than those of Hani, but there was not any significant difference between these two restaurants regarding their costumers’ continuing visits costumers’ evaluations.The findings of present study could be employed by the restaurant holders to improve their marketing strategies. Also, students of hospitality and tourism as well as 5 individuals interested in the field might get some insights covering the findings of the presentstudy.