Rice leaf miner Hydrollia prosternalis and the leafhopper Balclutha hortensis are considered key pest of rice plants in Egypt. Field trails were carried out at EI-Serw Experimental Station, Damietta Governorate 1997 and 1998, seasons. Both species were mostly active during August and September of both seasons according to Ali 1978. Bleih (1980) and Ise (1979). The relationship between the changes in the population density of 8. hortensis and H. prosternalis and the prevailing corresponding weather factors in the two tested years revealed a significant positive relationship for the Day Mx. Temp. Insignificant negative effect was ob­tained for H. prosternalis when the mean relative humidity % was consid­ered. The effect of one degree of these factors for B. hortensis was about (+7.8, 6.5 and —3.4) for day maximum, minimum temperature and relative humidity and (6.95. 5.4 and — 3.4) for 1997. Similar trend was observed for H. prosternalis i.e. (+4.8, +3.0 and —1.4) and (+2.1, +2.9 and —2.1) for 1997 and 1998. respectively. The analysis showed that (28 — 31 ‘C) . (19-22 °C) and 62-72 RH.%) may be regarded as the optimum day max.. min. and relative humidity. respectively.