This study was conducted to investigate the diversity and possible factors that structure the distribution and abundance of fireflies along Sungai Teratak. Six sampling occasions were conducted from March to April 2014 where ten display trees were chosen as sampling stations. Species abundance and composition of fireflies and other insects were assessed by visual assessment and sampling with aerial net. Four Pteroptyx species were discovered with difference in relative abundance, namely Pteroptyx bearni (93.1%), Pteroptyx valida (2.2%), Pteroptyx malaccae (3.9%), and Pteroptyx tener (0.8%). The results of Shannon-Weiner index, H’ was 0.316, and Simpson’s index of diversity with the value of 0.131 indicated that the firefly at Sungai Teratak was low in diversity. Abundance of firefly varied significantly between the six sampling occasions (Kruskal-Wallis = 15.382, d.f. = 5, p <0.05) but shows no difference in abundance between the ten display trees (Kruskal-Wallis = 14.181, d.f. = 9, p > 0.05). The abundance of fireflies was found to be positively correlated to the abundance of other insects (Pearson’s correlation r = 0.740, p <0.05). Comparison of fireflies’ abundance on full moon and new moon nights showed no significant difference (Mann-Whitney U = 46.00, z = -0.326, p >0.05 and Mann-Whitney U = 25.50, z = -1.945, p >0.05). Although the abundance of male (n= 232) firefly outnumbered the female (n= 149), statistical analysis proved no significant difference between both group (Mann-Whitney U = 8.50, z = -1.529, p >0.05). The mangrove trees being colonized by fireflies at Sungai Teratak was mainly from the species Avicennia alba.