All signs of the disease disappeared in one patient, and in 14 others there was evidence that cancer cells had died.
University of Surrey researchers said the virus could "help revolutionise treatment" for the cancer and reduce the risk of it recurring.
A bladder cancer charity called the study "very exciting" if larger studies confirmed the findings.
Non-muscle invasive bladder is the 10th most common cancer in the UK, with around 10,000 new cases each year.
Current treatments for this type of bladder cancer are invasive or can cause serious, toxic side effects.
And constant, costly monitoring is needed to check that the cancer has not returned after treatment.