Bowel Cancer UK says conducting more tests sooner would help as it is one of the most common causes of cancer-related deaths in the UK.
In Wales, a national bowel screening programme aims to reduce the number of bowel cancer deaths by 15% by 2020.
The Welsh government is spending an extra Â£4m to improve diagnostic tests.
The charity's report said the situation in Wales was "particularly poor" with 15% of patients waiting between eight and 14 weeks, and 26% waiting over 14 weeks for a colonoscopy, an internal bowel examination, when they are suspected to have problem.
A Welsh government spokesman said: "Nine out of ten patients newly diagnosed with cancer via the urgent suspected cancer route start treatment with in our 62 day target. This includes having diagnostic tests.
"When talking about general diagnostic waits, that exclude cancer, the eight week wait for specified diagnostic waiting times in Wales is a target which we expect to be met and sustained as a standard.
"To achieve this we have recently given health boards an extra Â£4m to improve diagnostic tests in Wales. We expect to see significant improvement over the next few months."
The charity also highlighted data from a national colonoscopy audit which it says showed the rate of colonoscopies conducted in Welsh health units fell "woefully short" of the UK average of 32.2 procedures per 100,000 of population with a figure of 23.3 in Wales compared to 46.8 in Scotland.
In Wales, a national bowel screening programme offers a test kit to men and women aged between 60 and 74 to help with early diagnosis of any problems.
Public Health Wales runs the Bowel Screening Wales service in line with other national programmes, including Breast Test Wales and Cervical Screening Wales.
The Bowel Cancer UK report, Right test, right time, says people across the UK are waiting significant lengths of time between being referred and having their test.
It says figures for England show less than 2% waiting more than the recommended waiting time whereas in Scotland performance has dropped, with 6.8% waiting longer than the recommended six week waiting time target.
The health service in Northern Ireland had not met its target of no patient waiting more than nine weeks, according to the Bowel Cancer UK report.
Waiting times for tests are "poor" for patients suspected of having bowel cancer in Wales and others parts of the UK, says a charity.