en Mathematical Modeling and Applications of OR Mathematical Modeling and Applications of OR پژوهشی Original <span style="font-size:11pt"><span style="line-height:115%"><span sans-serif="" style="font-family:Calibri,"><span style="font-size:12.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">In cost efficiency models, the capability of producing observed outputs of a target decision making unit (DMU) is evaluated by its minimum cost. Traditional cost efficiency models are considered for situations where data set is known for each DMU, while, some of them are imprecise in practice. Several studies have carried out to evaluate cost efficiency using fuzzy data envelopment analysis (DEA) methods for dealing with the imprecise data that have drawbacks. The issue of presenting improve strategy is ignored for inefficient units, as well as the applied models are not easily implemented. This paper proposes a new extension to evaluate fuzzy cost efficiency using fuzzy extended multiplication and division operations. This method offers a fully fuzzy model with triangular fuzzy input-output data along with triangular fuzzy input prices. In the proposed extension, a new definition of fuzzy cost efficiency is suggested based on the extended operations. Finally, a numerical example is provided to show the applicability of the proposed models.</span></span></span></span></span></span><br> &nbsp; Data Envelopment Analysis, Decision Making Unit, Cost Efficiency, Fuzzy Sets. 187 201 http://iors.ir/journal/browse.php?a_code=A-10-1431-5&slc_lang=en&sid=1 jafar pourmahmoud pourmahmoud@azaruniv.ac.ir 00031947532846002777 00031947532846002777 Yes Azarbaijan Shahid Madani University,