Objective  To investigate the association of digit ratio with single nucleotide polymorphism (SNP) at three loci (rs17576, rs3918249, rs9509) of matrix metallopeptidase 9 (MMP-9) gene.   Methods  A total of 804 Ningxia Han youths (399 males and 405 females) were used as the study subjects. A digital camera was used to take frontal photographs of the hands, and image analysis software was used to mark the anatomical points and measure the lengths of each finger of both hands (2D, 3D, 4D, 5D); Multiplexed PCR was used to detect the three polymorphic sites of the MMP-9 gene, SPSS 25.0 and R Studio software were used for data analysis and plotting.   Results  The 2D/3D (P<0.05) and 2D/4D (left,  P<0.01, right,  P<0.05) of both hands, 2D/5D (P<0.01), 3D/5D, 4D/5D (P<0.05) of the right hand, and 3D/4D (P<0.05) of the left hand in female youths of Ningxia Han were significantly higher than those in males, Differences in genotypes and allele frequencies at all 3 loci of the MMP-9 gene were not statistically significant between genders (P>0.05). Right hand 2D/4D was significantly associated with genotypes at the rs17576 and rs3918249 loci in male youths (P<0.05).    Conclusion  MMP-9 gene SNPs (rs17576 and rs3918249) may be associated with the formation of 2D/4D of Ningxia Han male youths. 

 Matrix metallopeptidase 9, Genetic polymorphism, Digit ratio, Anatomical measurement, Multiplex PCR, Ningxia Han youth