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To evaluate the relationship between intramammary infection and basic characteristics of mammary secretion at late dry period, regarding mammary secretions, macroscopic observations, infection status, somatic cell counts (SCC), serum albumin concentrations, immunoglobulin (Ig) G1, and IgG2 levels were examined on 20 dairy cows at 9–12 days before calving. Intramammary infections were found in mammary secretions from 37 of the total 80 quarters. All of the mammary secretions with intramammary infection showed lower viscosity than that of normal colostrum. In four mammary secretions without intramammary infection, some macroscopic abnormalities were found. For mammary secretions without intramammary infection or macroscopic abnormality, viscosities were apparently higher than that in normal colostrum, indicating that viscosity is associated with macroscopic normality of the mammary secretion at approximately 10 days before calving. SCC and serum albumin concentrations were significantly higher in mammary secretions with intramammary infection or macroscopic abnormality. The SCC and serum albumin concentrations were correlated with viscosity of the mammary secretions, suggesting that most intramammary infections at approximately 10 days before calving may cause mastitis with increased permeability of the blood–milk barrier. No significant difference was observed in concentrations of IgG1 and IgG2, regardless of the presence of intramammary infections or macroscopic abnormalities.