Journal of Applied Sciences1812-56541812-5662Asian Network for Scientific Information10.3923/jas.2011.3515.3519AshrafiA. JaafarA. B.1220111120Data Envelopment Analysis (DEA) is a non-parametric method for evaluating the efficiency of peer Decision Making Units (DMUs) with multiple inputs and outputs. During the last few years, a great number of DEA studies have focused on two-stage production systems where all outputs from the first stage are intermediate products that make up the inputs to the second stage. In these production processes, however, both desirable and undesirable factors may be present. Obviously, undesirable factors in production process should be reduced to improve the performance. In this study, a two-stage DEA model was proposed to improve the performance of stages by increasing undesirable inputs and decreasing undesirable outputs. A real numerical example was used to illustrate the model.]]>Laha, A. and P.K. Kuri,20116377388Amirteimoori, A., S. Kordrostami and M. Sarparast,2006180444452Amirteimoori, A.,20081147157Charnes, A. and W.W. Cooper,19629181186Charnes, A., W.W. Cooper and E. Rhodes,19782429444Chen, Y., W.D. Cook, N. Li and J. Zhu,200919611701176Chen, Y. and J. Zhu,20045922Coli, M., E. Nissi and A. Rapposelli,201111737742Fare, R., S. Grosskopf, C.A.K. Lovell and C. Pasurka,1989719098Ghorbani, A., S.A. Mirmahdavi and E. Rahimabadi,200932532Armagan, G.,20083325330Kao, C. and S.N. Hwang,2008185418429Rayeni, M.M. and F.H. Saljooghi,20101029452949Seiford, L.M. and J. Zhu,19994512701288Seiford, L.M. and J. Zhu,20021421620Sexton, T.R. and H.F. Lewis,200319227249Taher, A.H. and A. Malek,2009941744178Vencheh, A.H., R.K. Matin and M.T. Kajani,2005163547552Wang, Y.M. and K.S. Chin,20103787998808Zandieh, M., A. Azadeh, B. Hadadi and M. Saberi,2009910011013Zhu, J.,2000123105124Rayeni, M.M., G. Vardanyan and F.H. Saljooghi,20101028752880