Objective: This study aims to analyses the optimal size of government expenditure in Palestine over the period (1996-2020) and determine the optimal size of this expenditure through the reflection of this expenditure on achieved economic growth rates. Methodology: It was reached to the results by theoretical analysis and quantitative standard, The Researchers using mainly the Canonical Cointegrating Regression (CCR), Dynamic Ordinary Least Square Method (Dynamic OLS) and Fully Modified Least Square Method (Fully-Modified OLS) by following the methodology which used by Hajaya and Edie Nat (2017) and Scully (1998 - 2003) based on the work of Barro (1990). Results: The study found that the Palestinian government could have increase the public expenditure as a share of GDP to the proportion (17.7%) - if it were following a balanced budget and the absence of budget deficit which constitute the optimal size of public expenditure that offers the best contribution to improving growth rates economic. This difference between optimal expenditure proportion and the proportion of the real current expenditure is a decrease in the efficiency of expenditure could have been achieved by the government in the absence of those financial problems. Recommendation: The study concluded with a set of recommendations, the most important of which are rationalizing and reducing government spending and raising its efficiency, and on the other hand, searching for flexible and permanent sources of government funding. Keywords: The optimal size of Expenditure, The Government Expenditure, The efficiency of expenditure, Palestine