In today’s competitive business world customers are considered to be kings. Customers have several choices to make among alternative products, and they exercise a high level of influence in the market with respect to product size, quality and price. Hence, it is important for producers to meet the needs of customers in order to stay competitive. One of the marketing communication tools that is used in attracting the attention of the customer and build their loyalty is sales promotion. The aim of this paper therefore is to determine the effect of sales promotion on customer loyalty in the telecommunication industry. In this study, the survey method was used in gathering information from the respondents. Simple random sampling was used to select a sample size of 310, while descriptive and inferential statistical analyses were conducted with the aid of SPSS software. Producers spend a large part of their total marketing communication expenses on sales promotion. Hence, this paper attempts to find the effect of sales promotion on customer loyalty using a sample of customers of mobile telecommunication services. The paper found that, there is positive relationship between sales promotion and customer loyalty. More importantly, it was discovered that non-loyal customers are more prone to switch to competing products as a result of sales promotion than loyal customers.