This study has been conducted to explore the deceptiveness of advertisement by telecom service provider in Pakistan and its effect on the customer loyalty. Data have been collected from individual users of all the telecom service providers in Pakistan. The results of the study reveal that the telecom service providers are involved in deceiving the customer by falsely presenting the information in their advertisement and this factor is effecting the customer loyalty and customer satisfaction as well. Moreover the analyses of the data shows that females are more sensitive about the information presented in the advertisement and thus are more affected by this phenomenon than male.