This study was conducted to determine the effect of RWUE under different dates of planting and mulching treatment during rabi, 2017-18 in the Instructional-Cum-Research (ICR) Farm of Assam Agricultural University, Jorhat. The variety – Kufri Jyoti was grown in split plot design with 3 dates of planting (P1- 10th Nov, P2- 20th Nov and P3- 30th Nov) in main plots and mulches (M0- non mulch, M1- water hyacinth and M2- black polythene) in sub-plots, following recommended agronomic practices. Microclimatic parameters like daily soil temperature (5 cm and 10 cm depth) and soil moisture content at 10 days interval from two depths (0 - 15cm and 15 - 30 cm) were recorded throughout the period of experiment. A total of 98.1 mm rainfall was received during the growing period and weekly average BSSH ranged from 1.3 to 9.2 hr. Irrespective of mulching treatments, the highest tuber yield of 112.8 q/ha was recorded in first date of planting (P1), which was reduced by 11.68 and 14.22 per cent in second (P2) and third (P3) planting dates, respectively. The obtained result indicated that highest tuber yield of 120.8 q/hawasrecordedunder water hyacinth, followed by black polythene (103.5 q/ha) and non-mulched treatment (85.0 q/ha). Increased in tuber yield under water hyacinth was 42.12 per cent, while it was only 21.6 per centunder black polythene as compared to nonmulched condition. In potato cultivar Kufri Jyoti, irrespective of planting dates and mulching treatments the rain water use efficiency (q/ha/mm) varied from 2.72 to6.85 q/ha/mm with the overall mean of 4.60 q/ha/mm. Irrespective of mulching treatments, the highest RWUE was recorded in first date of planting (P1) and lowest was recorded under second date of planting (P2) of 4.81 q/ha/mm.