A method for estimating the population size of the Palestinians in West Bank (WB) and Gaza Strip (GS) is proposed. Given the fact that the only comprehensive census in these two areas was made by the Israeli Occupation Authorities in  1967, our method is based on a mathematical model and on some reliable figures such as the numbers of students in schools taken from these two areas. Sensitivity is studied, in particular   elasticity between the estimated  size of the   considered population and its growth rate, has been discussed. Finally, Several comparisons were made between our estimates and those made by four main Israeli sources. Three levels estimates were calculated, namely the minimum, medium and maximum of population size in WB and GS. These three levels are estimated up to the year 2010 . Thus our proposed model can serve as a flexible substitute for an absent census or/and as a concrete basis for any future census.