Gastric early-stage signet ring cell carcinoma (SIG) has been reported to have a lower rate of lymph node metastasis and a higher rate of favorable prognosis than other histological types. However, the development and progression mechanisms of early-stage SIG (early SIG) are controversial. This study examined the correlation between the mucin phenotype of early SIG and its clinicopathologic factors, particularly for the sake of less invasive surgery. Sixty-nine early SIGs were studied immunohistochemically with gastric mucin (M1 and MUC6) and intestinal mucin (MUC2). SIGs were classified into gastric (G), intestinal (I), gastrointestinal (GI), or unclassified (U) type. The intramucosal spreading patterns of SIG were investigated and then classified as either expansive or infiltrative. SIGs were classified into G-type (59.4%) and GI-type (40.6%). Neither the I- nor the U-type was observed. The GI-type expression correlated with the depth of tumor invasion in SIGs (P < 0.05). In contrast, there was no increase in GI-type expression in relation to tumor size. Intramucosal infiltrative growth correlated with intestinal metaplasia (IM) of background mucosa of SIGs (P < 0.01). There was no significant correlation between phenotypes and intramucosal spreading pattern. In conclusion, the GI-type expression of SIG is a clinically useful factor for predicting submucosal invasion. The findings of SIG surrounded with IM revealed the need to exercise great care in determining the surgical margin.