In the Global War on Terrorism (GWOT), the post-9/11 Pakistan’s alliance with the US has become an important subject of discussion and analysis in and outside the country. This study makes an attempt to examine and analyse comprehensively the costbenefit calculus for Pakistan as a result of its role in the US-led GWOT. Its basic premise is the hypothesis that Pakistan incurred more costs than benefits it accrued in this relationship. This is verified by using the exploratory research with qualitative method through inductive logic which is based on empirical data analysed through descriptive analysis. The paradigm of realism is used to explain these relations in their cost-benefit context. It also reviews the historical background of the US-Pakistan relations to contextualize and understand the nature of their bilateral cooperation during this period. It is noteworthy that from 1947 to 2001, these relations enjoyed two phases of close cooperation i.e. from1954 to 1962 and from 1979 to 1990 during which Pakistan derived great benefits but also paid huge costs for its cooperation with the US. These relations had reached their lowest level till 9/11 due to the US-imposed three-tier nuclear as well as democracy-related sanctions on Pakistan during 1990s. However, the events of 9/11 once again changed the dimensions of their relations particularly in the wake of the US decision to start GWOT from Afghanistan forcing the government of General Pervez Musharraf in Pakistan to cooperate in this war. During this war, Pakistan made tremendous efforts and huge sacrifices due to which it considerably won the appreciation from the US-led Western alliance. However, the US continued making demand from Pakistan to ‘do more’ to eliminate the terrorists sheltered in safe havens and sanctuaries in Pakistan, as blamed by the US, Afghan government and India, which the latter always denied. This tension continued haunting Pakistan-US relations during this period with periodical vicissitudes. But, the operative dynamics of the anti-terrorism cooperation kept these relations working in which, as premised, Pakistan suffered more losses than the benefits it accrued.