Abstract We conducted a series of hydraulic fracture initiation tests with fractured natural rock samples. The objective is to characterize the interaction between hydraulic fracture initiation and natural fracture infiltration and opening. The natural fracture was simulated by cleaving a rock cube into two or three layers and putting the parts back together. The hydraulic fracture is initiated by pressurizing the borehole drilled perpendicular to the layers. The test parameters include rock type (sandstones and a tight limestone), confining stress and fluid type (silicon oil and cross-linked gel). A detailed model was built to simulate the hydraulic fracture interaction with a natural fracture. Qualitative agreement was found with the test results.