The researches were conducted in the climatic chamber and in the greenhouse of the Institute of Soil Science and Plant Cultivation – State Research Institute in Puławy, in Mitscherlich pots filled with a mixture of soil and sand in the amounts of 5 and 2 kg, respectively. The first  experimental  factor was  the variety of lupine: Legat – determinate genotype and Polo – indeterminate genotype. The second factor was air temperature in the period of lupine flowering and pod setting: optimal (night/day: 14/24^oC) and raised (night/day: 18/30^oC). It was found that high temperature at flowering caused  a change in the course of some phonological phases of yellow lupine. Plants which were growing at increased temperature considerably earlier ended flowering and began pods setting, as well as ripened some days earlier than plants which grew at optimal air temperature. Exposure of plants to the high temperature conditions caused an increase of plants height and a reduction of leaf area and vegetative organs weight. Both varieties of yellow lupine which were included in the researches were characterised by similar content of chlorophyll in leaves, and high temperature significantly decreased its value. Lupine var. Legat (determinate genotype) produced lower mass of vegetative and generative organs than plants var. Polo (indeterminate genotype). High temperature at flowering had a negative effect on seed yield value, however this concerned the Legat variety to a greater degree than the Polo variety. The decrease of seed yield of yellow lupine which grew at higher air temperature conditions was a consequence of lower number of pods and seeds per plant and significant decrease of 1000 seeds weight.