Primitive upland cultivars (Oryza sativa L.) were collected in northern Laos. One-hundred-thirty-two cultivars were collected in upland fields at 27 sites. Morphological and physiological traits were recorded. The materials were classified into indica and japonica types based on isozyme genotypes. We classified 106 japonica, 16 indica, two intermediate, and eight heterozygous cultivars. The japonica cultivars were characterized by glabrous hulls and sticky grains. Only two out of 16 indica cultivars were glabrous. The heterozygotes were estimated to be generated by out-crosses between japonica and indica cultivars in upland fields. The intermediate type would be the progeny of such heterozygotes. Higher polymorphism was found at two isozyme loci—Amp1 and Est2—among the japonica cultivars. Genotypic frequencies differed between populations collected from upland fields along roads and along a branch of the Mekong river. Such differences would be caused by different origins of these two populations. In this report, isozymes were indicated as valuable markers to recognize the cultivars to be of independent stock.