Reticular or lattice-like perineuronal coatings of condensed extracellular matrix (ECM), termed perineuronal nets (PNs), enriched in proteoglycans (PGs) and/or glycoproteins (GPs) were demonstrated to ensheath cell surfaces of certain neuronal circuits in the central nervous system (CNS) of mammals, reptiles and fishes. In the present study, the histochemical and quantitative characteristics of postnatal ECM in the retrosplenial cortex (RSC) of albino rats were described with a cationic iron colloid (CIC) or with CIC-Bodian's technique for detection of sulfated PGs and with certain plant lectins from Vicia villosa agglutinin (VVA), Wisteria floribunda agglutinin (WFA) or Glycine max agglutinin (SBA) for demonstration of N-acetylgalactosamine containing GPs. The differentiating PNs were shown to make their development as early as 1-2 weeks postnatally (Pw1-2), which surround the surface of some neurons distributing throughout the II-V cortical layers. During the first postnatal month and onwards, the net-encapsulated neuronal cells underwent progressive increment in number and presented an inside-out pattern of migration and differentiation throughout the V-II cortical layers. At a later stage (Pw6-8), the overall density and intensity of labeled PNs progressively increased and reached the adult stage of development. In addition, they displayed their differential labeling characteristics for the lectin/CIC double staining, which were differentially identified into three types, namely; PGs-, GPs-, and PGs/GPs coats. The morphometric investigation revealed that the total density of net-associated retrosplenial neurons (RSNs) at Pw2 was about 1.80±0.29 /UA (UA = 60.15 µm2) after labeling with the WFA/CIC double staining technique, and this variant increased polynomially with progression of postnatal age reaching 9.12±1.82 /UA at Pw12. Quantitative analysis showed that the gain of net-associated RSNs increased rapidly during the first postnatal month (2.86 fold), and then increased 1.73 fold during the second month, but increased 1.02 fold at the third month. Statistical analysis revealed that throughout the postnatal period, the numerical density of net-associated RSNs increased significantly with advance of age (R = +0.992; P<0.01). In addition, the numerical densities of PGs- and GPs-coated neurons, as well as those exhibiting coat complexes (PGs/GPs coats), increased polynomially with progression of animal age (R = +0.996, +0.990 and +0.976, respectively with P < 0.01 in all parameters). At Pw2, the absolute numerical density of RSNs labeled with VVA, WFA, SBA, CIC and CIC-Bodian's staining measured about 2.12±0.17, 1.80±0.13, 0.00, 0.00 and 3.00±0.18 /UA, respectively. These parameters increased significantly with postnatal age and respectively reached 6.18±1.23, 5.00±1.03, 2.90±0.69, 3.85±0.76 and 4.30±1.13 /UA at Pw12 (R = +0.995, +0.995, +0.997, +0.996 and 0.984 with P<0.01 for all parameters). In addition, labeling indices of RSNs stained with the aforementioned staining at Pw2 was 3.60, 2.94, 0.00, 0.00 and 3.52, respectively. These variants increased significantly with advance of animal age reaching 15.84, 12.82, 7.43, 9.87 and 11.02, respectively (R = +0.994, +0.997, +0.998, +0.996 and +0.999 and P< 0.01 for all variants). This finding indicated that the perineuronal ECM components are significantly correlated with age and suggest a possible developmental and biological significance including promotion of migration and functional maturation of net-associated neurons in the RSC. In addition, the finding of present study would be contributed as baseline for future experimental or environmental studies that are expandable for other mammalian species including the human.