The 40S ribosomal protein S29 (RPS29) was shown differentially expressed in deltamethrin (DM)-susceptible and resistant Culex pipiens pallens previously. Here, we cloned RPS29 from this mosquito. An open reading frame (ORF) of 171 bp was found to encode a putative protein with 56 amino acid residues, which shares more than 90% identities with other mosquito RPS29 genes. Moreover, quantitative real-time PCR analysis demonstrated that the transcriptional level of RPS29 was significantly up-regulated both in DM-resistant Cx. p. pallens and C6/36 cells compared with the susceptible ones. Over-expression of RPS29 showed a slight decrease of cell viability in DM-susceptible C6/36 cells under DM treatment and knockdown of RPS29 by siRNA comparably increased cell viability in DM-resistant cells. Our study provides evidence that RPS29 might be associated with fitness cost of DM resistance in mosquitoes for the first time.