Tight junctions (TJs) play crucial roles in tissue homeostasis and inflammation through their roles in the control of paracellular transport and barrier function. There is evidence that these functions are compromised in older organisms, but the exact mechanisms leading to TJ deterioration are not well understood. Claudin proteins are a family of membrane proteins that constitute the structural barrier elements of TJs and therefore play a major role in their formation and function. Using immunohistochemistry and immunoblotting, we have studied the expression of six different claudin proteins (claudin-1, -2, -3, -4, -5, and -7) in three tissues (liver, kidney, and pancreas) of aging male and female mice. In general, we find an age-dependent decrease in the expression of several claudin proteins in all three tissues observed, although the exact changes are tissue specific. Our findings provide a possible basis for the decrease in tissue barrier function in older organisms.