Seventy-eight patients with gastric cancer were underwent MRI to investigate whether the histogram analysis of the entire tumor volume in ADC maps could differentiate between histological grades. A series of histogram parameters were calculated and correlated with the histological grade of the surgical specimen. There were significant differences in the 5th, 10th, 25th, and 50th percentiles, skew, and kurtosis between poorly and well-differentiated gastric cancers. There were correlations between the degrees of differentiation and histogram parameters, including the 10th percentile, skew, kurtosis, and max frequency. Histogram analysis of the ADC maps can be useful in differentiating between histological grades.