Research studies of institutionalized children have shown severely reduced performance in different areas of mental development. Most of these children are born preterm, however there are a limited number of studies which considered the child gestational age in their analysis. The current study evaluates the mental development of two groups of late preterm infants (30-36 weeks of gestation) raised in a typical institution with care as usual (N = 27), and a family-like institution (N = 16) characterized by stability, sensitivity and responsiveness of the primary social-emotional environment. The BDI (The Battelle Developmental Inventory) is used to assess developmental skills of preterm children. The comparative analysis of infants' development assessed at 3 and 9 months of age is presented. Research data reveal no differences in mental development between the two groups of late preterm children at 3 months of age; conversely, at 9 months of age preterm children from the family-like institution (after 4-8.5 months of institutionalization) have a significantly higher level of personal-social, communicative, adaptive, motor, cognitive and general behavioral development in comparison with their peers from the typical institution. Results are discussed in terms of influence of quality social-emotional environment on infants' mental development from groups of biological risk.