Fibromatosis of mesentery is a very rare disease and only a few cases have been reported. Here we report a case of 40 year old man admitted on 16 October, 2017 in the Department of Surgery (Unit-3) of Mymensingh Medical College Hospital with history of recurrent abdominal pain and progressively enlarging intra-abdominal lump for 2 years. Out of different diagnostic dilemmas, finally we came to the conclusion of its being a mass lesion primarily arising from the mesentery and involving the adjoining gut according to the report of CT abdomen. Laparotomy was performed and a lump measuring about 18 cm × 20 cm arising from mesentery was found, in which distal part of jejunum and proximal part of ileum were embedded. The mass was excised with incorporated gut loops and histopathology report revealed fibromatosis of mesentery.