The present study was carried out at Rabbit Research Unit, Agricultural Researches and Experiments Station, Faculty of Agriculture Mansoura University, EL-Mansoura, Egypt, during the period from December 2013 to December 2014. This study aimed to examine the effect of increasing level of fat in the diet of does and bucks of New Zealand and California rabbits on their reproductive performance. The rabbit does and bucks within each strain (New Zealand White and California) were divided into two groups. The two groups were assigned at random to receive one of the two experimental diets which were formulated to be similar in DE but vary in EE. First group was fed on a commercial diet containing 3% fat (Control).Second group was fed on a diet supplemented with sunflower oil (rich in omega 6) to increase EE content to 6%. The following mating system was as follows: -          Treatment 1: bucks 3% inseminated does 3%. -          Treatment 2: bucks 3% inseminated does 6%. -          Treatment 3: bucks 6% inseminated does 3%. -          Treatment 4: bucks 6% inseminated does 6%. Reproductive performance of does (number of service per conception, litter size and litter size weight at (birth, 21 days and weaning and mortality rate at (21 days and weaning) were recorded. In general, results show that increasing fat in the rations of bucks or does or both led to significant decrease in litter size at birth, 21 days and weaning compared to bucks and does fed control ration containing normal fat level. This was also accompanied by a significant decreased in weight of litter size. The results show higher number of services per conception in all treatment than the control ration. It is worth noting that average percentages of mortality rate at 21 days and weaning were significantly (P<0.05) higher in rabbit buck or does or both treated with high level of fat than those fed on the control ration in New Zealand and California rabbit pups. In conclusion, the addition of high level of fat (rich in omega 6 - sunflower oil) has reduced litter size, increased number of services per conception and increased mortality rate. This finding needs further studies to determine the effect of high level of fat on the parameters studied. This may be accomplished by measurement of fatty acid differentiation in blood plasma, follicular fluid and seminal plasma. In addition, measurement of pH value of vagina and seminal plasma could explain the effect of high level of fat on number of services per conception. While, analysis of does milk and anatomy of died pups could explain the higher mortality rate.