The Finn came second in the Spanish Grand Prix on Sunday but was on form on Tuesday morning as he topped the timesheet in a time of 1:16.525s. Charles Leclerc came home second 0.797s behind Bottas with Carlos Sainz almost an entire second further back.
Sebastian Vettel and Sergio Perez were both testing for Pirelli during the session and recorded times of 1:18.425s and 1:19.79s respectively. The pair were testing to help with the development of the tyres for 2020.
There were also drives for Pietro Fittipaldo, who finished above Sergio Perez, Nick Yelloly making his first F1 appearance in three years and Callum Ilott. Nicholas Latifi also got a run out in the Williams as rumours circulate about him being lined up to take over from Robert Kubica. Nico Hulkenberg finished bottom of the leaderboard during the opening sessions as Renault continue to struggle.