Jan Blachowicz is a professional Polish mixed martial artist who competes in the light heavyweight division. A professional MMA competitor since 2007, Błachowicz has mostly competed for KSW, Poland's biggest promotion, where he is their current light heavyweight champion.

Błachowicz entered in KSW's first <95 kg (209 lbs.) tournament at KSW 9. Defeating three opponents in one night, Błachowicz was able to claim the tournament crown. His first opponent was Martin Zawada, who he defeated by unanimous decision. Błachowicz was able to defeat his next two opponents by armbar. Błachowicz went onto defeat Christian M'Pumbu four months later via armbar, before defeating previously unbeaten Maro Perak in December 2008.

Looking to expand his horizons after a very successful year 2008, Jan accepted an invitation from Tomasz Drwal and joined him at the Throwdown Training Center in San Diego for a few months. He agreed to temporarily fight at heavyweight, against Lloyd Marshbanks under the War Gods banner, but the event was cancelled. Despite suffering a serious knee injury in July, Jan continued his training, as he agreed to fight "somewhere in Mexico". About three weeks later, his knee suddenly popped in training when executing a takedown. The anterior cruciate ligament in his right knee was destroyed, making a knee reconstruction after his return to Poland inevitable.

Jan was planning his comeback fight in March against Aleksander Radosavljevic at WFC 10, but decided to withdraw and was replaced by fellow teammate Antoni Chmielewski. After finally returning from the knee injury and a 17 month layoff, Błachowicz entered into the second KSW <95 kg tournament. Błachowicz had to face two opponents in the same night. His first opponent was the undefeated Brazilian Julio Cezar de Lima whom he was able to knock out with a high kick-right hook combination at 3:40 in the first round. In the semi-final, Błachowicz submitted his training partner Wojciech Orłowski with a rear-naked choke after just 1:37.

At KSW 14 Blachowicz faced Daniel Tabera in the final of the tournament, winning via TKO in the second round and once again becoming the KSW Light Heavyweight Tournament Champion. Błachowicz then faced Rameau Thierry Sokoudjou for the vacant KSW Light Heavyweight Championship at KSW 15. He lost the fight via TKO, being unable to answer the bell for the third round. Błachowicz rematched Sokoudjou at KSW 17, once again for the title. He won the bout via unanimous decision and became the new KSW Light Heavyweight Champion. Jan later defened his belt at KSW 20 against Houston Alexander, defeating Alexander by unanimous decision.

Blachowicz's next title defense came against Goran Relic, whom he defeated via unanimous decision to retain his title.