In this Study four Sandstone rocks were drilled by diamond core bit using a fixed laboratory-drilling machine at 400 and 1200 rpm, rotary speed, over a range of weights on bit (WOB) 12,18,24,30,………kg. Operating parameters of the drill bit such as WOB, penetration rate (PR), torque (T), and specific energy (SE)were continuously monitored during the drilling trials. Besides the effects of formation properties on the penetration rate were monitored. Relationships between WOB and both PR, torque T and Se were described and the relationship between PR and SE was given. Graphs are presented and can be used to predict diamond-drilling performance easy and fast.