This study investigated selenoprotein P expression, using immunohistochemistry, in gastric adenocarcinoma tissue microarrays constructed from 30 gastric adenocarcinoma specimens and 30 normal gastric tissues (controls). Selenoprotein P expression scores were significantly lower in gastric adenocarcinoma (17/30, 56.7%) than in control tissues (25/30, 83.3%). Selenoprotein P was significantly more likely to be expressed in well-to-moderately differentiated cases (13/17, 76.5%) than in cases with low differentiation (4/13, 30.8%) and there was no significant difference in selenoprotein P expression between tumour node metastasis (TNM) stage I - II (11/19, 57.9%) and TNM stage III (6/11, 54.5%). In conclusion, selenoprotein P expression was low in gastric adenocarcinoma tissues compared with control tissues and was related to the degree of gastric adenocarcinoma differentiation but not to TNM stage.