Physiological traits can be used to improve the efficiency of selecting suitable genotypes to grow under nitrogen (N) limitation. The objective of the current study was to investigate the relationship between physiological characteristics and storage root yield of three cassava genotypes under three rates of N fertilizer. The experiments were conducted from 2014 to 2016 at farm fields in Thailand. A split-plot randomized complete block design with four replications was used. Three different rates of N fertilizer, i.e., 46.9, 90.0 and 133.2 kg N/ha and three cassava genotypes, Rayong 9, Rayong 11 and Kasetsart 50, were used. Kasetsart 50 had the highest mean performance for most crop traits. Growth rate of stem (SGR), storage root (SRGR) and crop (CGR) during 180-210 days after planting (DAP) and leaf area index (LAI) at 120 DAP were related to storage root dry weight for all three rates of N fertilizer. Storage root growth during 90-120 DAP, CGR during 180-210 DAP and specific leaf area (SLA) at 210 DAP contributed most to storage root dry weight of the three genotypes grown at 46.9 kg N/ha, while the combination of SRGR during 90-120 DAP, SRGR during 180-210 DAP, LAI at 210 DAP and SLA at 210 DAP was best for N fertilizer at 90.0 kg N/ha and the combination of leaf growth rate (LGR) during 180-210 DAP and LAI at 210 DAP was best for N fertilizer at 133.2 kg N/ha.