Nineteen speedboat crew members were given urine tests for drugs and two crew from different boats tested positive.
Further tests on the urine samples will determine whether the positive signs were caused by illicit drugs or legal medication.
One speedboat was found to lack insurance.
Marine Police have been conducting drugs tests and document checks at beaches and piers around Phuket as part of a campaign to ensure the safety of tourists on Phuket.
The focus has been on jet-ski operators, mostly at Patong where the majority of jet-skis are based, and on day-trip speedboat crews.