The polymorphism of AChE1 and over-produced esterases were analyzed in 18 field samples collected from Tunisia between 2002 and 2005. An AChE1 insensitive to propoxur inhibition was detected in all samples, with the exception of the sample # 18. The highest frequencies of the resistant phenotypes ([RS] and [RR]) (>0.83) were detected in the samples # 2, 3, 5, 6, 9, 13, 15, and 17. The highest frequencies of [RR] phenotype were recorded in samples # 9 (0.83) and 6 (0.75). This phenotype was absent in three samples (# 7, 14, and 18) and had a frequency ranged from 0.03 to 0.3 in the rest of the samples. The [RS] phenotype was present in all the samples, with the exception of the sample # 18, with a frequency ranged from 0.08 to 0.86, and > 0.75 in the samples # 3, 5, 15, and 17. The frequency of [SS] phenotype ranged from 0 in the sample (# 9) to 1 in the sample (# 18). Five esterases of high activity were observed in studied field samples. The esterase C1 encoded by the Est-1 locus and four esterases encoded by the Ester super locus: A1, A2-B2, A4-B4 (or A5-B5, which has the same electrophoretic mobility) and B12. One or several esterases were detected in all the studied samples, with the exception of the sample # 18. Results were discussed in relation to resistance mechanisms and Culex pipiens pipiens control.