Abstract: Knowing the sex of embryos produced for use in an embryo transfer program can assist farmers in managing their resources more effectively. With an objective of determining the relationship between embryonic development rate and sex ratio of the in vitro produced (IVP) bovine embryos, a total of 930 oocytes divided into 2 groups (excellent and good) according to their morphological score, time of first cleavage and the rate of blastocyst formation were employed. The proportion of embryos that cleaved before 36 h post insemination (pi) was significantly higher (P < 0.05) in each group compared with slow cleaving (cleaving after 40 h pi) embryos (55.6 and 50.2% Vs 29.3 and 27.8%, for excellent and good, respectively). Moreover, fast cleaving embryos yielded higher (P < 0.05) percentages of fast growing embryos (i.e., those that reached blastocyst stage within the fist 7 days of culture: 30.5 Vs 18.7%, for excellent- and good-classified oocytes, respectively). Although there was no significance difference among groups in terms of cleavage time, oocytes from the excellent group showed a significant increase (P < 0.05) in total blastocyst rate compared with those originating from group classified as good (32.6 Vs 20.7, respectively). There was no significant difference between fast and slow growing embryos with regard to their sex ratio. Both fast and slow growing embryos biopsied either at 8-cell or at > 8-cell stages showed a significant (P < 0.05) different sex ratio from the expected 1:1. The overall sex ratio was 77 Vs 23% for male and female respectively, from both developmental groups probably due to the type of sperm used and/or both cultural and manipulation conditions. These results suggest that although there might be some differences in developmental rate between male and female embryos, such phenomena are associated with other factors such as the source of sperm as well as cultural conditions. As such, more studies are needed to clarify this aspect.