A field experiment was conducted to evaluate the performance of three Chinese flaxseed (Linum usitatissimum L.) genotypes (Longya-10, Longya-14, Longxuan-1,) against local check Ilsi-90 under varying levels of NPK and boron fertilization in the agro-climatic conditions of Sindh, Pakistan. The study followed a factorial randomized complete block design with three replications and five fertilizer treatments: Five fertilizer treatments were applied: F₁ (control) with 0-0-0 NPK + 0.0 kg B ha⁻¹, F₂ with 50-30-20 NPK + 0.5 kg B ha⁻¹, F₃ with 75-45-35 NPK + 1.0 kg B ha⁻¹, F₄ with 100-60-50 NPK + 1.5 kg B ha⁻¹, and F₅ with 120-75-50 NPK + 2.0 kg B ha⁻¹. Data were collected on agronomic traits (plant height, branches per plant, capsules per plant, 1000-seed weight, grain yield, and oil content), as well as nutrient concentrations in leaves and seeds (N, P, K, and B). The results revealed that the combined application of 100-60-50 NPK + 1.5 kg B ha⁻¹, especially in the genotype Longya-14, significantly improved all measured parameters. Longya-14 consistently recorded the highest plant height (78.5 cm), branching (17.0), capsules per plant (12.0), seed weight (7.5 g), grain yield (1089.3 kg ha⁻¹), and oil content (40.12%), along with superior concentrations of N, P, and K in both leaf and seed tissues. Significant treatment × variety interactions were observed for seed potassium and boron content and for leaf phosphorus, potassium, and boron concentrations. These results indicate that balanced NPK fertilization with boron, in combination with nutrient-responsive genotypes like Longya-14, can enhance flaxseed performance and seed nutritional quality under field conditions.