Display omitted •Incorporating QTL information will increase the accuracy of breeding value.•At position 235 cM on chromosome 1, one QTL affecting weaning weight identified.•The QTL found in this study could be related to muscle depth gene.•Validation of this QTL helps to select higher genetic potential rams and ewes. This study aimed to detect the quantitative trait loci (QTL) which affecting the growth traits in some parts of chromosomes 1 of Sanjabi lambs. The study population consisted of six groups of fathers which had an average of 39.17 lambs. Initially, the fathers were genotyped for eight microsatellite markers on chromosome 1, and the offspring of the heterozygote fathers were genotyped. The quantitative traits were the body’s weight at birth, 3, 6, 9, and 12 months, which were corrected for the fixed effects of year of birth, sex, and birth type. QTL search was performed by interval mapping based on a regression model for each cM (Centimorgan) of the chromosomes. In total, one QTL in the 235 cM of chromosome 1 was identified from the beginning of the chromosome in associate with weaning weight. The sire substitution effect for both families was 2.14 kg. The confidence interval estimation of the detected QTL that was estimated using the Bootstrap method was 225–238 cM of chromosome 1. This QTL was determined between the MCM137 and MCM130 markers and at a distance of about 9 cM from the MCM137 marker. If this QTL was approved in the next research, it can be used in Marker-assisted selection programs. In this case, more accuracy should be achieved for the evaluation of superior animals.