In Vietnam, Casava plants (Manihot esculenta Crantz) is one of the most important food-plants beside rice and maize plants and is also the important incomes of the poor households. Many researches in the world as well as in Vietnam claimed that plant density of casava had significant influence on the yield. The research was implemented in Bao Yen district - Lao Cai province to detennine the effiency of planting KM94 casava variety and the optimum planting density for the casava production status of this area. The research results showed that the best planting density for KM94 variety in Bao Yen district - Lao Cai province was 15,625 plants/ha. The casava plants also had the highest yield of fresh tuber (35.4 tons/ha) and the highest interest (36.74 millions VND/ha). Therefore, it is recommended that the famers use this planting density for KM94 variety in the area of Lao Cai province.