An FDNY firefighter landed in jail Friday evening after getting into a fight with his cousin, cops said.

The familial fisticuffs began at the firefighter’s house in Brooklyn’s 70th precinct — which covers the Midwood and Kensington neighborhoods — at about 8 p.m. on Friday, authorities said.

Firefighter Juan Lopez, 30, allegedly scratched his cousin’s neck as the two fought, prompting the cousin to call 911, said cops, who nabbed Lopez on an assault charge.

It was not immediately known what the two were fighting about.

The FDNY did not immediately return request for comment.