A catheter lock solution which is a catheter lock preparation having a bacteriostatic property at physiological osmotic pressure without practically containing a bacteriostatic component such as a preservative, an antimicrobial agent, or an antibiotic and having high safety, characterized in that the preparation contains a weak acid having an acid dissociation constant (pKa) of 3.0 to 6.5 as a buffer, a pH of the solution is less than 6.0, preferably from 3.0 to about 5,5, an osmotic pressure ratio is from 0.5 to 3.0, and a pH change (variation) can be suppressed to less than the 6.0 with the weak acid, and a container containing the catheter lock solution.
