Gastrointestinal stromal tumours (GIST) are the most common mesenchymal tumour of gastrointestinal tract and the stomach being the most commonly involved organ. Focal calcification may be seen in GIST but prominent or heavy calcification is rare. Gastric mass with prominent calcification on imaging may create a diagnostic dilemma. We present a rare case of gastric GIST with heavy calcification in a 55 years old female presenting with abdominal lump. Computed tomography (CT) showed a large heterogenous juxta gastric mass with solid-cystic component with heavy calcification. She underwent laparotomy and en-bloc gastric sleeve resection with the mass. Microscopic examination showed tumour with spindle cell and calcification with mitotic index of 6/50 High power field. Immunoreactivity with Vimentin, CD34 and DOG 1 confirmed diagnosis of GIST. Dystrophic calcification of necrotic or degenerative tissue is thought to be cause of calcification in GIST. Very few cases of heavily calcified GIST have been reported in literature, our case is of interest because presence of solid cystic component and a huge size ~ 14 cm (longest diameter).