We analyzed patterns of geometrid species richness in South Korea to assess the observed and estimated species richness gradient, to determine predictors for the distribution of moths and to investigate the effect of latitude on the species richness of moths in the Korean peninsula. The species richness was analyzed for 541 geometrid moths across 17 quadrates, with each quadrate defined by one degree of latitude and longitude. Two subgroups of geometrid moths were adopted according to their distributional ranges: Palearctic (435 species, 80.4%) and Oriental (106 species, 19.6%). To investigate the relationship between the distribution of geometrid moths and environment, eight variables were used. The estimated species richness of geometrids was calculated using the Chao 2 estimator because there was uneven sampling effort across the quadrates. Due to multicollinearity we used covariance values produced by principal component analysis and the first four axes adopted have eigenvalues >= 1.0. Two models of regression analyses were applied based on multiple linear regression using eight variables (model I) and principal components axes (model II). Of the two subgroups of geometrid moths the Palearctic species richness increased with latitude, but not that of Oriental species richness. A combined effect of abiotic (maximum altitude, temperature, rainfall, and latitude) and biotic (plant species richness and vegetation) variables was indicated by both models of regression analyses. The different effect of each spatial and environmental predictor on the distribution of geometrid moths on the Korean peninsula is discussed. The significant relationship between estimated species richness and latitude indicate a peninsular effect on geometrid moths in South Korea.