SEE  ALSO
BODY BUILDERS	FIGHTERS

In 2009, Pudzianowski signed a contract with Konfrontacja Sztuk Walki – a Polish mixed martial arts organization – to take part in four fights.

He debuted as a mixed martial arts fighter on December , 2009, during the KSW 2 event in Warsaw, Poland, winning against Marcin Najman, a professional boxer (who, at that time, was also a MMA newcomer). Pudzianowski started throwing low kicks soon after the fight began. After several hits, Najman fell to the mat and Pudzianowski started delivering punches (a tactic known as ground-and-pound). Najman was forced to tap the mat, indicating he wanted to end the fight, which lasted for only 43 seconds. Before the fight Mariusz said: "Lewa ręka niesie za sobą śmierć, a prawej sam się boję." (English: "The left hand brings death, but the right one even I am afraid of.")  Pudzianowski collected 200,000 złoty (70,000 USD) for the fight.

On May 7, 2010, during the KSW 3 event, Pudzianowski won his second fight, against Yusuke Kawaguchi. The fight lasted two full rounds, with Pudzianowski winning by judges' decision. The fight was described as a "sloppy brawl". It was noted Pudzianowski had control over most of the fight, but was "neutralized" by Kawaguchi, and that, by the second round, he was looking "to be out of energy and breathing heavily".

On May 2, 2010, Pudzianowski went on to participate in the Moosin: God of Martial Arts event, where he fought former two time UFC Heavyweight Champion Tim Sylvia. Pudzianowski fractured his metatarsus during the first round and then went on to deplete his stamina during the rest of the fight, which ultimately led to Sylvia defeating him via submission (punches) at :43 of round 2.

Following his loss to Sylvia in May, Pudzianowski signed to face former heavyweight boxer and kickboxer Eric Esch, better known as 'Butterbean', at KSW 4 on September 8. After several brief standup exchanges, Pudzianowski secured a takedown early in the fight and was then able to dominate Esch with ground and pound. Esch, unable to get back to his feet during the attack, tapped out to the strikes, making Pudzianowski the winner by submission at :5 of the first round. He came into the fight notably slimmer, having lost around 20 lbs from his previous fight. Many believe his large muscle mass to have caused his stamina problems in his earlier fights.

On May 2, 2010 Pudzianowski fought James Thompson at KSW XVI, losing by arm triangle.

In September 20 Mariusz Pudzianowski started professional training in the well known MMA camp in the USA – American Top Team.

Pudzianowski fought on the KSW XVII event, which was held on November 26, 2011. He faced James Thompson in a rematch. He won the fight via majority decision. This decision caused controversy as Thompson had virtually full control in both rounds, and after the fight Thompson, who was clearly angered by the decision, took the microphone from the announcer and launched a verbal assault directed at the promotion in which he ranted: "F**king joke. Give Mariusz a big round of applause. Come on. What a f***ing joke. I thought KSW was really trying to be serious. If you can watch that back and call that serious, then (looking at the promoter) you're f***ed, and KSW is going down the f***ing toilet." Two days later the promotion changed the result to a No Contest. During a conference held on November 28, the ruling was deemed to be a "judge's error" and the fight result was changed.

Mariusz's next opponent was Bob Sapp. The fight took place in Lodz, Poland on KSW 9. Mariusz won via a TKO in the first round, battering Sapp with a barrage of punching and securing a takedown followed with more punches to win just 39 seconds into the fight.

Mariusz then faced Christos Piliafas on September 5 in the main event of KSW 20. Mariusz won via TKO in the first round, after dominating Piliafas on his feet, he then secured a takedown followed by posturing up and raining down some ground and pound to win at 3:48 seconds into the fight.