The Southeast Asian country has vaccinated 92.31 percent of its population of 16 million against the coronavirus, one of the highest vaccination rates in the region, official data shows.
Prime Minister Hun Sen said the new rules would start from Thursday and should help boost tourism and business.
"Now it's the stage to open the economy by learning how to live with Covid," Hun Sen said in a speech.
Foreign visitors would still need to be fully vaccinated and those unable to show proof of vaccination would need to be remain in quarantine for 14 days after arrival.
Even with the removal of mandatory testing, authorities called on visitors to test themselves.
"The Ministry of Health would like to urge all travellers that they should do rapid tests," Health Minister Mam Bunheng said in a statement.
Authorities also plan to resume issuing visas on arrival, which were suspended during the pandemic, though the statement from the health ministry did not confirm when this would start.
Cambodia, which reported 140 new coronavirus infections on Wednesday, has registered 3,049 deaths in total due to the virus.
International arrivals plummeted to 113,000, or a 90.6 percent fall, in the first seven months of 2021, compared with the same period in the previous year, the World Bank said.
Similarly, entrance fees collected from Cambodia's famed Angkor temple complex plunged 98.7 percent to $236,000 over the period.
Tourism accounted for two million jobs and contributed to a quarter of the country's gross domestic product before the pandemic, the World Bank said.