The aim of this study was to determine the effect of behavioral reactivity on maternal behavior of ewes and early postnatal behavior and growth in lambs until weaning. The study was carried out with 100 multiparous Norduz ewes and 30 lambs. The study began by performing arena and scale tests and determining the test cortisol level in ewes during the anestrus period. Then, ewes were divided into two groups according to test reactivity as either “reactive” or “proactive” by using hierarchical cluster analysis. On the 50th day after mating, 15 reactive and 15 proactive gestating ewes of similar live weight, body condition and age (54.5 ± 0.58 kg, 3.19 ± 0.023 points and 4.07 ± 0.089 years, respectively) and carrying a single fetus each were selected and placed in one of two groups. Behavior of ewes and lambs from each group were monitored for a 3 -h period post-partum and the ewe-lamb separation test was performed within first 3 days postnatal. Ewes were phenotyped according to grooming duration, number of bleats, leaving lamb, preventing sucking etc., while lambs were phenotyped based on number of successful sucks, bleats, total suck duration, etc. Growth was determined by recording live weights of lambs at 2-week intervals until the 90th day. The whole trial lasted a total of 9 months. Ewes grazed entirely on rangeland with no extra feed supplementation. Ewes were fed with alfalfa hay and gradually supplemented with barley and concentrate during the winter. Serum cortisol levels were found significantly different in reactive and proactive ewes (1.57 ng/ml and 0.86 ng/mL, respectively; p < 0.001). During the early postnatal period, more high-pitched bleats were counted for proactive ewes, who also left their lambs alone more often than reactive ewes (p < 0.01), whereas reactive ewes had higher scores for following during ewe-lamb separation tests (p < 0.05). Lambs of reactive ewes had a higher total number of successful sucks, longer sucking duration (p < 0.05), and better growth performance at day 30 and day 45 (p < 0.05) as compared to lambs of proactive ewes. However, the weaning weights of reactive and proactive lambs were found similar as 30.3 ± 1.01 vs 30.2 ± 0.71 kg, respectively. In sum, the results of the present study indicated that some early postnatal ewe-lamb behaviours, ewe-lamb separation test score and lamb growth may be associated with behavioral reactivity. Given these findings, it was concluded that behavioral reactivity has potential use in efforts to improve maternal care and lamb welfare.