Physiological traits responsible for differences in yield performance among pre-released genotypes are normally not known. The objective of the present study was to evaluate seasonal variations in dynamic growth and development traits between 12 large-seeded Virginia-type and 14 small-seeded Spanish-type advanced breeding lines of peanut (Arachis hypogaea L.). The experiment was conducted in 1999 and 2000 at Khon Kaen University in Northeast Thailand for three planting dates, representing the early-rainy season, mid-rainy season and dry season. Very similar phenological development was observed for all lines within each group and between the early and the mid-rainy seasons. However, a lower temperature during the early growth stage in the dry season delayed flower initiation and extended maturity. During this period, crop growth rates as well as the development rate for leaf area index and specific leaf area were also lower compared with the rainy seasons. On average, both pod yield and total biomass for the rainy season and the dry season were about the same. Variations among lines within each group were also small. For these advanced breeding lines, the pod growth rate was the most important yield determinant while the crop growth rate had lesser effect and the partitioning coefficient and pod-filling duration had no significant effect. However, the crop growth rate, pod growth rate and partitioning coefficient were important traits for a line to be the top yielder. Pod-filling duration was also important when the lines involved were considerably diverse in maturity and seed size. Information on these traits, if used together with final pod yield, will make varietal selection more efficient.