A field study was conducted at Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur, in summer season during February to August 2014 to know the seasonal fluctuation pattern of insect pests and natural enemies in brinjal ecosystem. The major insect pests were found in brinjal field viz. jassid (136.02 per 10 leaves), whitefly (92.88 per 10 leaves), aphid (83.33 per 10 leaves) and brinjal shoot and fruit borer (20.44 male moth per trap-week) and their highest population was observed at 70, 85, 70 and 116 days after transplanting (DAT). Epilachna beetle, leaf beetle, green leaf hopper and leaf roller indicated as the relatively minor pests of brinjal. Average temperature showed significant positive correlation with the population of jassid, whitefly, aphid, brinjal shoot and fruit borer and epilachna beetle. While average relative humidity had a significant negative correlation with population of jassid, whitefly and aphid. A significant negative correlation was also observed in case of rainfall for white fly and aphid. Natural enemies found in the brinjal field were spider, black ant, lady bird beetle, carabid beetle, syrphid fly and preying mantid.