Two field experiments were conducted during 2011/2012 and 2012/2013 seasons at Agron. Dept. Farm., Fac. Agric., Assiut Univ., to study the response of lentil to foliar application of potassium phosphate under different irrigation treatments.The results showed that: Irrigation treatments had a highly significant influence on the all studied traits except harvest index in both seasons. So, plants had one irrigation (I₁) at flowering (after first irrigation, Mohaya) produced the highest mean values of all studied traits except harvest index in both seasons. Also, plants had twice of foliar application of potassium phosphate produced the highest mean values of all studied traits. The interaction between irrigation management and foliar application of potassium phosphate had a significant effect on all studied traits except harvest index and protein % in both seasons. Plants had received twice of foliar application of potassium phosphate with I₁ treatment produced the highest mean values of plant height (47.34 and 45.36 cm), number of branches plant^-1 (4.52 and 4.25), number of pods plant^-1 (46.25 and 44.35), seed yield plant^-1 (1.46 and 1.42 g), seed index (26.57 and 27.05 g), seed yield plot^-1 (1.78 and 1.76 kg), straw yield plot^-1 (6.43 and 6.65 kg), and seed yield fed.^-1 (712.0 and 704.0 kg) in the first and second seasons, respectively