Summary High seminal reactive oxygen species (ROS) are related to poor semen quality and impaired fertilization. We aimed at finding whether there is an association between ROS and fertilization, embryo quality and pregnancy rates after conventional in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). In prepared semen of 147 male partners of infertile couples, ROS were assessed with luminol chemiluminescence. Spermiogram was assessed in native semen. ROS were negatively correlated with standard sperm characteristics and testicular volume, and positively with abnormal sperm head morphology. Fertilization rate and embryo morphology on day 2 and on day 4 were assessed in 41 IVF and 106 ICSI cycles. The influence of maternal (female age and number of oocytes) and paternal (sperm motility, morphology and ROS) factors on fertilization and embryo quality were assessed by means of regression analyses. After IVF, fertilization and pregnancy rates were negatively associated with ROS level (p = 0.031 and 0.041, respectively). In case of higher ROS, significantly fewer ICSI‐derived embryos (p = 0.036) reached the morula‐blastocyst stage on day 4. High seminal ROS levels are associated with impaired sperm fertilizing ability and lower pregnancy rates after IVF. In ICSI, a negative association of ROS with embryo development to the blastocyst stage has been observed.