Intravesical drug administration is used to deliver cytotoxic agents through a catheter to treat bladder cancer. One major limitation of this approach is poor retention of the drug in the bladder due to periodic urine voiding. Mucoadhesive dosage forms thus offer significant potential to improve drug retention in the bladder. Here, we investigate thiolated silica nanoparticles retention on porcine bladder mucosa in vitro, quantified through Wash Out50 (WO50) values, defined as the volume of liquid necessary to remove 50% of the adhered particles from a mucosal tissue. Following irrigation with artificial urine solution, the thiolated nanoparticles demonstrate significantly greater retention (WO50 up to 36 mL) compared to non-mucoadhesive dextran (WO50 7 mL), but have weaker mucoadhesive properties than chitosan (WO50 89 mL). PEGylation of thiolated silica reduces their mucoadhesion with WO50 values of 29 and 8 mL for particles decorated with 750 and 5000 Da PEG, respectively. The retention of thiolated silica nanoparticles is dependent on their thiol group contents and physical dimensions.