The aim was to compare the effect of dimethylacetamide (DMA) and N-methylacetamide (NMA) concentrations on the quality and fertility of post-thaw chicken semen. Ejaculates were obtained from 30 Hi-Line White roosters and processed according to the following treatments: lake pre-freezing extender + 0.1 M trehalose (LPF-T) + 6% DMA (control treatment), LPF-T + 9% DMA, LPF-T + 6% NMA, and LPF-T + 9% NMA. Sperm quality (viability, motility, and kinetic traits) was assessed before and after cryopreservation. A total of 15 laying hens per treatment were inseminated to assess fertility and embryo viability. Sperm cryopreserved in presence of DMA had significantly better in vitro quality compared to NMA, showing the highest proportion of viable and progressive motile sperm recovered after thawing. Furthermore, proportion of progressive motile sperm and the VCL, LIN, ALH, and WOB mean values were significantly improved in semen samples frozen/thawed with 6% compared to 9% cryoprotectant concentration. However, the best cryoprotective action on sperm quality played by DMA and the lowest cryoprotectant concentration did not translate into a concomitant advantage in in vivo semen fertility that showed no differences between cryoprotectant and cryoprotectant concentration treatments. Finally, the cryoprotectant DMA and NMA showed an opposite effect on embryo viability in comparison with the effect played on in vitro semen quality, being NMA more efficient than DMA on preserving viable embryos. The present results suggest the urgency to further decrease the cryoprotectant concentration in poultry semen freezing procedures and to assess the specific toxic effect of cryoprotectant on sperm integrity, fertility, and embryo development., (© 2019 Poultry Science Association Inc.)