Flaxseed (Linum usitatissimum L.) is a minor crop in Chile. There is interest to increase the number of crops on the current rotation in South Central Chile and also to increase oilseed feedstocks for salmon feed. There is little information published about seed yield and oil content response to N, P, and K fertilizers on flaxseed in Chile. The objective of this study was to determine the effect of N, P, and K fertilization on flaxseed yield, oil content, and composition. The study was conducted at two locations during two growing seasons (environments), in Chillán 2004-2005, 2005-2006, and in Osorno 2004-2005, 2006-2007. Treatments were four levels of N (0, 100, 200, and 300 kg N ha-1), three levels of P (0,100, and 200 kg P2O5 ha-1), and two levels of K (0 and 150 kgK2O ha-1). The design was a randomized complete block with a factorial arrangement of three factors (N, P, and K) and four replicates. According to the results, flaxseed yield improved as N rates increased. Physical optimum rate (rate at which maximum seed yield is obtained) was different depending on the location and year. Nitrogen rate increased oil content and yield up to 200 kg N ha-1. Oil composition was not affected by N, P, and K rates, or their interactions. The P and K nutrients did not have an effect on seed yield, oil content, oil yield, and oil composition.