As Pakistan has high revenue expenditure gap and one of the lowest taxes to GDP ratio, the government is unable to finance its expenditure and is dependent upon borrowing which resulted in huge debt. This study is focusing on analyzing the structural changes in the economic structure that have weakened the tax structure (both elasticity and Buoyancy) in economic history. Tax elasticity is a measure designed for measuring the response of tax revenues to changes in output after controlling for exogenous shocks including the discretionary changes. Whereas the tax buoyancy measures the response of tax revenues mobilization to growth in national output. A tax is considered to be buoyant if the growth in tax revenues rises more in proportion to the increase in national output. The overview of Pakistan's tax system of over the period till 2004 reflects a very grim picture. The tax elasticity of the total tax revenue had been recorded less than unity, both with respect to the total GDP and the non-agricultural GDP. Moreover, it has also been observed that in the case of buoyancy the coefficients were low, reflecting that the tax changes did not lead to significant revenue changes. Various methodologies had been adopted overtime for estimation of elasticity and buoyancy coefficients. To tackle the issues of a unit root in time series data under consideration, the Autoregressive Distributive Lag Model has been used. The estimates of elasticity and buoyancy obtained for all major taxes in Pakistan has been less than unity depicting that the changes in income have not been reflected in the tax collection