Hammers of hammer mill are changed when working edges are worn but, often this is not decided according to the quality standards of feed and their possible effects on performance. The aim of the present work was to study the effect of different hammer status (new; N or worn; W) on particle size distribution of ground diets and the performance of weaned piglets. One hundred sixty 28-d-old piglets [Pietrain × (Landrace × Large White)] were distributed into 16 pens according to their initial BW following a RCBD. A pre-starter (PS; 0 to 14d) and a starter (ST; 14 to 35d) diet was formulated to contain 2.63 Mcal/kg NE, 20.2% CP, 1.37 Lys and 2.48 Mcal/kg NE, 15.1% CP, 1.20 Lys, respectively. Two experimental treatments were performed according to the hammer status N or W. PS and ST diets were ground at Ø = 2 and Ø = 3 mm, respectively. Feed was offered ad libitum in mash form. Individual animal weight and feed disappearance were recorded at 0, 14, and 35 d post-weaning to calculate average daily feed intake (ADFI) and average daily gain (ADG). Data were analyzed with ANOVA taking into account block of BW and hammer status as main factors. Feed particle size distribution was determined as % of particles ≥1 mm, ≥0.75 mm, ≥0.5 mm and <0.5 mm. Different size distribution was mainly observed for ST. The W diets showed 21% and 3.7% more particles of ≥ 1mm and ≥ 0.5mm, but 8.5% and 9.3% less of ≥0.75 mm and <0.5 mm, respectively than N diet. For PS period, no different BW, ADG and ADFI was observed (P > 0.05). However, higher ADFI (666 vs 619 g/d; P = 0.03) and a tendency to higher ADG (418 vs 387 g/d: P = 0.10) were observed for the animals fed the N diet for ST period. Considering the entire period (0 to 35d), higher BW (18.9 vs 18.1 kg; P = 0.03), ADFI (505 vs 471 g/d; P = 0.01) and ADG (318 vs 295 g/d: P = 0.03) were observed for the animals fed the N diets. It is concluded that hammer status affects particle size and piglet performance in weanling diets in a larger extend in ST than PS diets.