The behavior of cellular beam is described using design methods according to BS: 5950, considering particularly the strength of tee sections and web post element. Such behavior is derived from parametric study involving finite element analysis using software ANSYS. The design method is based on plastic analysis of beam section at ultimate loads and elastic analysis at serviceability loads. The procedure of design of cellular beam is illustrated and an example based on design method is worked out and its verification is done for checking the suitability.