Abstract: Forty-day-old healthy piglets were co-infected with porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2). The changes of mRNAs of cytokines in porcine alveolar macrophages (PAM) of the inoculated piglets were analyzed using a real-time fluorescent quantitative PCR (real-time FQ-PCR). The results showed that the transcriptions of IFN-γ mRNAs exhibited two transcription bottoms at day 3 and 28 post-inoculation (PI) and a peak at 7DPI and 42DPI respectively, with significant differences at 3DPI and 7DPI (P<0.05). The transcriptions of IL-12p40 mRNAs reached the highest level at 7DPI, with significant differences at 3 DPI and 14DPI (P<0.05), and then downregulated at 28 and 42DPI with no significant differences. In addition, the mRNAs transcriptions of IL-10 peaked at 14DPI with significant differences at 3DPI (P<0.05), 7DPI (P<0.05) and 14DPI (P<0.01), then declined gradually to the level of the control at 42DPI. Accordingly, the co-infection of PRRSV and PCV2 could significantly activate the transcriptions of IL-12p40 and IL-10 mRNAs early during the co-infection, while the transcription of IFN-γ mRNAs witnessed more kinetic changes, an indication of the impairments of cellular immune response, immune regulatory and anti-infection function of PAM in dually infected piglets.