The estimation of effectiveness factor for the case of wave shell catalyst is attempted through an approximated procedure developed by the authors for other kind of catalytic pellets. It is shown that the approximate scheme ran be used even with this kind of important catalysts and that the results so obtained are very accurate. The analysis is only restricted to the case of single reaction although it can be used even for those cases where non-isothermal conditions could prevail. The estimation avoid the solution of the governing mass and heat balance differential equations by numerical procedures. Finally a set of algebraic equations must be solved through an iterative scheme which is illustrated for the case of isothermal systems.