Mice that were selected for over 108 generations for body weight at the postnatal (PN) day 21 were examined in the open field (OF) test and in the Lashley maze (LM) for their exploratory behavior and spatial learning. Light (L), heavy (C) and control (K) lines of mice in three age groups: PN-21, PN-56 and PN-90, were tested once in the OF and three times in the LM. During the session in the OF the L mice displayed a steady increase of behavioral activity (sum of locomotion and rearing, climbing, sniffing, and grooming acts), whereas mice C and K habituated in the last stage. During entire session in the OF activity of the L mice was lower than that of the C and K mice. The L mice displayed high defecation/urination scores. In the learning task the L mice performed worse than the C and K mice. In conclusion, behavior of the L line was different from that of the two other lines: they showed higher anxiety and poorer spatial learning.